Hi. Im 16 years old and i have not had a period for 4 months now. When i was getting a period it was normal to a heavy flow on some days. Ive taken many at home pregnancy tests and they all say negative. I haven't gained or lost any weight. I moderately exercise for about an hour a day and eat healthy (always have). I'm no more stressed then usual. I've been on birth control for about a year and a half now. So I was wondering what the problem could be?