Suggest Remedy For Absence Of Menstrual Bleeding

I am 19 and don't have my period. I had some bleeding in eighth grade but nothing since. I've seen my doctor about it and they said I'm developing fine everywhere else, just slower than usual. I was nervous though, so they did an ultrasound and said everything looks fine. We did blood tests of some sort which were supposed to determine whether or not my ovaries are healthy...they told me they are. They also determined that my brain is communicating properly with my reproductive organs and that it's nothing to do with my hypothalumus (right?). The doctor gave me these pills to take for 10 days and said I should have some bleeding at the end. I did, but again, it was really light. She says everything is fine though. But if it's all fine, why don't I just menstruate then? I've heard of Premature ovarian failure...do you think i have that? or something else? or do you agree that i could just be fine?