If you don't get your period every month as expected or don't get your first period by the time you are 15, it is called amenorrhea.
Amenorrhea means you do not have menstrual periods. There are two types. Primary amenorrhea means you never start your periods. Secondary amenorrhea means you have had periods, and then they stop, especially for more than 3 months.
Amenorrhea can happen for many reasons. Sometimes it’s caused by a problem with the reproductive organs or another medical problem. Other times it’s caused by doing hard exercise for long periods of time. It can also happen if you don’t eat well or if you diet too much or have an eating disorder. Pregnancy and certain types of birth control can also delay your periods.
Your doctor will want to find out why your period hasn’t started. You may need to make some diet and exercise changes. These may help start your period. Or you may need treatment for another problem.