I haven't had my period in a few months and I know I'm not pregnant. What's wrong with me? – Alyssa* It's not unusual to miss periods or to have an irregular menstrual cycle — especially in the first couple of years after you've begun having your period. Many girls also notice changes in the flow and duration of their periods from month to month. Irregular and missed periods are common, but if you were having regular periods before or if you have not had a period in more than 3 months, talk to your doctor. Some medical problems (such as hormone imbalances) and lifestyle changes (such as stress, too much exercise, or large amounts of weight loss or gain) can cause girls to miss their periods. Your doctor will be able to look into the cause of any possible problems. *Names have been changed to protect user privacy. Back to Articles Related Articles Tampons, Pads, and Other Period Supplies When it comes to pads and tampons, there are lots of choices. It may take some experimenting before you find what works best for you. Here are some tips. Read More Irregular Periods Wondering whether it's normal to have irregular periods? Get the facts about this common problem. 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.