missed periods but not pregnant

Hello and thank you for choosing EmpowHer,
It is very common in adolescent years to have an irregular period. One thing to be careful of as a vegetarian though, is getting enough iron. Red meat offers a lot of iron which is important for the female menstrual cycle to be regular. So, I suggest that you take iron pills as a supplement. Even if you are not anemic, it is a great supplement to take in general for adolescent girls, especially vegetarians.
Secondly, just because you do not have a regular period, does not mean you are unhealthy or there is something wrong with your body. It's not necessary to have a regular period unless you are trying to get pregnant, or you have severe symptoms such as heavy, prolonged menstrual bleeding.
One indicator that you should see a doctor is severe PMS without menstrual bleeding. This may also be a sign of something more serious than simply hormonal imbalances.
In any case, doctors will usually prescribe birth control pills to teens with irregular cycles or severe symptoms. But if you are experiencing severe symptoms, taking birth control pills is not necessarily the answer. So, if you have severe symptoms and the doctor simply puts you on birth control, this is red flag! I highly suggest before accepting any treatment, that you receive a pap smear/pelvic exam, and even test for anemia, to make sure nothing more serious is going on.
Faith