It is very common for young women to have irregular periods for the first couple of years after their period starts. During the first year you should have a least 4 periods, the second year at least 6 periods, and for the 3-5th year, at least 8 periods a year. After that you should have a menstrual period about 21 to 35 days apart. Another reason a woman might not get her period is if she is pregnant. If you still haven’t gotten your period after a couple months or if there’s a chance you might be pregnant, make an appointment with your health care provider.
See the Menstrual Periods Health Guide for more information: https://youngwomenshealth.org/2010/04/21/menstrual-periods/