I'm 19 years old and my period has been irregular since I first got it 5 years ago. Is this normal?
– Clare*

It is normal to have irregular periods for the first few years of menstruating — and sometimes even longer. But the only way to know if everything's OK is to visit your doctor or . The length of a menstrual cycle can vary from girl to girl, but on average they are usually between 21 and 35 days.

A number of things can cause irregular periods: A girl may have something going on with her hormones. Excessive exercise, not eating enough calories, or being underweight or overweight can also affect a girl's menstrual cycle. So can medications or drugs (like steroids).

Since you've had irregular periods for more than 3 years, see your doctor or nurse practitioner to find out what's causing them. He or she may be able to prescribe medications to help correct a medical problem. Or, if things like exercise or eating habits are behind your irregular periods, your doctor may give you ideas for some changes.

Girls who are having sex (or have had sex in the past) should see their doctor once a year. Pregnancy or sexually transmitted diseases (STDs) can affect a girl's periods — and some STDs cause serious long-term complications, like infertility.

*Names have been changed to protect user privacy.