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 nurse practitioner . The length of a menstrual cycle can vary from girl to girl, but on average they're 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 cycle. So can medicines or drugs (like steroids). Because 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 medicines 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. *Names have been changed to protect user privacy. Back to Articles Related Articles Irregular Periods Wondering whether it's normal to have irregular periods? Get the facts about this common problem. Read More How Do You Know If Your Period Is Regular? Find out what the experts have to say. Read More STDs (Sexually Transmitted Diseases) You've probably heard lots of discouraging news about sexually transmitted diseases. The good news is that STDs can be prevented. Find out how to protect yourself. Read More Can a Girl Get Pregnant if Her Periods Are Irregular? Find out what the experts have to say. Read More My Periods Are Irregular. What's Going On? Find out what the experts have to say. Read More PMS, Cramps, and Irregular Periods Get the facts on which period problems are normal and which ones might indicate something's going on. Read More All About Periods Periods can be confusing. Get the facts in this article for teens. Read More Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor. © 1995-2021 KidsHealth®. All rights reserved. Images provided by The Nemours Foundation, iStock, Getty Images, Veer, Shutterstock, and Clipart.com.