Why did my period stop? is it ok?

im 16 and im in track. i weigh about 116ish pounds. i used to get my period every month until i joined track. ever since which is about 3-4months, i stopped getting my period. it worries me a lot... my doc said its ok but yea.. is it normal?Why did my period stop? is it ok?
Yes. It's because of the training. See, the way Mother Nature contrived it, we need a minimum body fat % in order to menstruate. The design behind that was, that women during a famine couldn't carry a child to term. It's like an insurance policy, that even if bad times came, there would be a bit put away to feed the growing fetus. You'll find, as soon as you regain a little body fat (just a couple % most likely) your period will come back.
Yes, this is normal. Many factors of your daily life can affect your cycle, one of them being excessive excercise, or an increase in excercise, which reduces your body fat. Becuase of track, your body fat has reduced, and we all have a minimal percentage of body fat that we need in order to menstruate. Think of it this way: our body is specially designed so that we are only allowed to get pregnant when our body is sure that we can keep a baby alive. By reducing body fat, our body senses that we cannot sustain ourselves, never mind another life. Anyways, once you stop track, your body fat will return to its normal level, and your period will come shortly after.