I am 18 and still a virgin. And I just started taking these diet pills because I have gained over 30 pounds since being out of high school. I missed my period and I don't know what could have caused it. Please help?

It could be the weight gain that caused you to miss your period. Or it is even possible that the diet pills caused this. Stress can cause this also.

You do not mention your age, but age can play a factor in missed periods also.

My gyno told me it's quite normal for women between the ages of 18-19 to have missed periods, no idea why but it's been said by others.

I think the real concern is that you're on diet pills.
:( Not good for your body at all!
I would rather be overweight then take something that is going to contribute to heart failure.

Weight loss and weight gain will cause you to skip periods and so will stress. Sometimes diet pills do cause stress as well. If you miss one period you are fine, mostly everyone will miss a priod once in a while but you should consult a doctor if you miss more than 3 consecutive periods.