Are you eating? One of my best friends stopped getting her period because she was too thin and not eating enough... I will also echo everyone else's answers and say go to the doctor!
Yea u need to go see a doctor u probably have PCOS I have it & would miss my periods for 4 to 6 months. Most likely they will just give u birth control to regular u out but u need to do it now b4 it gets worst cuz it will. Trust me.
Seek medical attention. Could be good news...
If you one birth control like "the pill" it can interfere with your menstrual cycle, To what ive heard anyway.