---
title: "Irregular periods: causes and when to see a doctor"
description: "Common causes of irregular periods, from contraception to thyroid problems, with clear advice on when to see a GP or get urgent help."
url: "https://myruva.co/learn/irregular-periods-causes-and-when-to-see-a-doctor"
language: "en-GB"
topic: "Your cycle"
published: "2026-10-18"
updated: "2026-10-18"
author: "Ruva team"
reading_minutes: 5
---

# Irregular periods: causes and when to see a doctor

Common causes of irregular periods, from contraception to thyroid problems, with clear advice on when to see a GP or get urgent help.

*Written and reviewed by the Ruva team · Updated 2026-10-18 · Your cycle*

Irregular periods can follow changes in contraception, stress or big weight changes. Pregnancy and conditions that affect hormones are other possible reasons. Irregular periods are not usually a sign of a problem. Still, the [NHS says to see a GP](https://www.nhs.uk/symptoms/irregular-periods/) if your periods are irregular or your usual pattern changes.

An early period, a long gap and spotting between periods are different changes. They can have different causes. [ACOG treats changes in timing, bleeding between periods and unusually heavy flow as separate things](https://www.acog.org/womens-health/faqs/abnormal-uterine-bleeding). Dates alone can't tell you the cause. You don't need to know the likely reason before you book an appointment.

If the gap between the start of each period is your main worry, [how long a normal menstrual cycle lasts](https://myruva.co/learn/how-long-is-a-normal-menstrual-cycle) compares the published ranges.

## Changes to take to your GP

Book a GP appointment if:

- Your periods are irregular, or your usual pattern has changed.
- Bleeding lasts longer than 7 days, or is unusually heavy.
- You bleed between periods, after sex or after menopause.
- You have missed three periods in a row.
- A missed or irregular period comes with other symptoms, such as weight changes, tiredness or new facial hair.
- Irregular periods are making it harder to get pregnant, if you want to.

These reasons come from the NHS advice on [irregular periods](https://www.nhs.uk/symptoms/irregular-periods/) and [missed periods](https://www.nhs.uk/symptoms/missed-or-late-periods/), and from [ACOG's bleeding guidance](https://www.acog.org/womens-health/faqs/abnormal-uterine-bleeding). [Pain or bleeding that stops you from doing everyday things](https://womenshealth.gov/menstrual-cycle/your-menstrual-cycle) also deserves help.

Bring whatever notes you already have. [Irregular cycles: what to log and when to ask](https://myruva.co/learn/irregular-cycles-what-to-log-and-when-to-ask) can help you put them in order. You don't need a complete diary before you book.

## Pregnancy, breastfeeding and a missed period

A missed period can be an early sign of pregnancy. Breastfeeding can also delay the return of your periods after birth. The [NHS missed periods guidance](https://www.nhs.uk/symptoms/missed-or-late-periods/) and the [Office on Women's Health cycle guide](https://womenshealth.gov/menstrual-cycle/your-menstrual-cycle) both explain this.

You may or may not ovulate while breastfeeding. If you want to avoid pregnancy, ask about suitable contraception. Having no periods does not mean you are protected. With irregular cycles you may ovulate less regularly, but you can still get pregnant.

If you could be pregnant after a missed period, take a test. Bleeding doesn't rule pregnancy out. [Bleeding from an ectopic pregnancy can be mistaken for a period](https://www.nhs.uk/conditions/ectopic-pregnancy/symptoms/). If you could be pregnant and have bleeding with pain, get advice quickly.

### When to test

If you don't know when your period is due, test at least 21 days after the last unprotected sex. If the result is negative and you still think you could be pregnant, test again a few days later. If the second test is negative and your period still hasn't come, contact your GP. Follow the [NHS pregnancy test guidance](https://www.nhs.uk/pregnancy/trying-for-a-baby/doing-a-pregnancy-test/) and the instructions that come with the test.

## Contraception and medicines can change bleeding

Hormonal contraception can change your bleeding. You may bleed when you didn't expect to. [Starting or stopping the contraceptive pill can affect your periods](https://my.clevelandclinic.org/health/symptoms/14633-abnormal-menstruation-periods). The NHS also lists the progestogen-only pill, the injection and the hormonal coil as possible causes of irregular periods.

Some changes affect how heavy your flow is more than when it comes. A copper intrauterine device (IUD) can make bleeding heavier, especially in the first year. Blood-thinning medicines and aspirin can also make periods heavier, as [ACOG's guide to abnormal uterine bleeding](https://www.acog.org/womens-health/faqs/abnormal-uterine-bleeding) explains.

Ask the person who prescribes your medicine or contraception what bleeding changes to expect with it. Tell them about new or troublesome bleeding, even if you think it's a side effect, so they can check it. Don't stop a prescribed medicine or change how you take your contraception without advice.

## Periods at puberty and approaching menopause

Periods are more likely to be unpredictable when they first start. The same goes for perimenopause, the years leading up to menopause. At these stages you may not ovulate regularly, and [cycles without ovulation can bring irregular or heavy bleeding](https://www.acog.org/womens-health/faqs/abnormal-uterine-bleeding).

As you get closer to menopause, you may miss periods and then bleed again. Your periods may also get longer, shorter, heavier or lighter. The [Office on Women's Health describes these changes through the reproductive years](https://womenshealth.gov/menstrual-cycle/your-menstrual-cycle).

Talk to a doctor about unusual or troublesome bleeding, even if changes are expected at your age. ACOG recommends this for the stages when irregular periods are common. Bleeding after menopause needs checking too. Treat it as a reason to get care, not as a period coming back.

## Stress, weight and exercise

Big weight gain or loss, stress and too much exercise are among the [possible causes of irregular periods](https://www.nhs.uk/symptoms/irregular-periods/). If you notice a stressful time or a change in your training, mention it at your appointment. There may still be another cause to check.

These changes are not your fault. Describe what has been going on. You can ask, “Could this change in my routine be part of it?” You don't have to prove a link first. You also don't need to start a diet or exercise plan on your own before you go.

For a closer look at the evidence for each one, read [stress, sleep, exercise and your cycle](https://myruva.co/learn/stress-sleep-exercise-and-your-cycle).

## Conditions your GP may consider

Polycystic ovary syndrome (PCOS) can affect ovulation and lead to irregular periods. Current [NHS guidance](https://www.nhs.uk/symptoms/irregular-periods/) calls it polyendocrine metabolic ovarian syndrome (PMOS). Some other guidance still uses the name PCOS. Thyroid problems can also affect when your periods come.

[An underactive thyroid and an overactive thyroid](https://my.clevelandclinic.org/health/symptoms/14633-abnormal-menstruation-periods) are both possible causes. Other conditions affect bleeding in different ways. ACOG lists fibroids and polyps, which are growths that aren't cancer, as causes of irregular or heavy bleeding.

Your GP can look at more than one possible cause. Tell them about any other symptoms you have along with the change in your periods. Tiredness, facial hair growth, weight gain and skin changes are especially worth mentioning. You don't need to have every symptom on a list to ask for help.

## Get urgent advice for these symptoms

If you could be pregnant, get [medical advice quickly, even without a positive test](https://www.nhs.uk/conditions/ectopic-pregnancy/symptoms/). This applies if you have unusual bleeding or pain low in your tummy, especially on one side. In the UK, contact a GP urgently or call NHS 111. Elsewhere, use your local urgent medical service.

Sudden, intense tummy pain with severe dizziness or fainting can be an emergency. Call 999 in the UK or your local emergency number. You can also go to an emergency department (A&E in the UK).

[ACOG also says to get emergency care](https://www.acog.org/womens-health/faqs/abnormal-uterine-bleeding) if you are changing pads or tampons every hour for more than 2 hours in a row. This applies when you also have chest pain, shortness of breath and light-headedness or dizziness. Get help straight away.

## Quick answers

### Why is my period irregular all of a sudden?

Possible reasons include pregnancy, changes in contraception, stress, big weight changes and conditions that affect hormones. A new pattern is worth talking about with a GP. Timing alone can't tell you the cause.

### Can you get pregnant if your periods are irregular?

Yes. Irregular periods can mean you ovulate less regularly, but you can still get pregnant. If you could be pregnant and don't know when your period is due, the NHS says to test at least 21 days after the last unprotected sex.

### How many missed periods should I wait before seeing a doctor?

The NHS says to see a GP after three missed periods in a row. Go sooner if your usual pattern changes or you have other symptoms. If you could be pregnant and have pain or unusual bleeding, get medical advice quickly.

## Sources

1. [Irregular periods](https://www.nhs.uk/symptoms/irregular-periods/), NHS
2. [Abnormal Uterine Bleeding](https://www.acog.org/womens-health/faqs/abnormal-uterine-bleeding), American College of Obstetricians and Gynecologists
3. [Your menstrual cycle](https://womenshealth.gov/menstrual-cycle/your-menstrual-cycle), Office on Women's Health
4. [Irregular Periods (Abnormal Menstruation): Causes & Treatment](https://my.clevelandclinic.org/health/symptoms/14633-abnormal-menstruation-periods), Cleveland Clinic
5. [Missed or late periods](https://www.nhs.uk/symptoms/missed-or-late-periods/), NHS
6. [Doing a pregnancy test](https://www.nhs.uk/pregnancy/trying-for-a-baby/doing-a-pregnancy-test/), NHS
7. [Ectopic pregnancy - Symptoms](https://www.nhs.uk/conditions/ectopic-pregnancy/symptoms/), NHS

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This guide is general information to help you keep and use your own records. It isn’t medical advice. If you’re worried about a symptom, or something changes suddenly, talk to a doctor, nurse or pharmacist.