Background: I started taking birth control pills when I was 13 for heavy periods, cramps, and depression along with a mild anti-depressant. I'm not 21 and I stopped taking them about a year and a half to two years ago.

Problem: Since then, I don't get my period. If I take one birth control pill, (just one, not a pack or anything) I'll get my period, but other than that, no period. I'm 90% certain that I'm not pregnant because I have no other symptoms, I don't have unprotected sex, and I don't have sex very often. I've also noticed my libido is low and once a week (or round about) I've noticed that when I stretch my stomach I'll get a sharp pain about where my ovary is (with reference to my anatomy textbook).
I don't want to go to my doctor because of the cost and time loss to go to a doctor's appointment unless there is a real problem that shouldn't wait.

History: I'm a 21 yr old white female of slightly under average height, over weight, daily mild exercise (walking and playing with two dogs) and two days of harder exercise. I've had the same male partner for 3 yrs.

Thanks for your time!