loss of period/menstrual cycle, anyone?

Sorry about all my questions lately. I was just wondering if this has happened to anyone else. My last period was on July 17, 2007. I'm a virgin so there's no possibility of pregnancy (they still made me take a pregnancy test when I went for my colonoscopy). I'm almost 18 1/2, 5'6" and in my first year of college. I've always been really thin...right now I'm around 86-90 pounds =( ...so it was expected that I'd get my period later than everyone else. I believe I got it at the beginning of my junior year of high school in September of 2005. Anyway, since July 17 I haven't had a period. I went to the obgyn in either October or November and she did an internal exam (my first one...so awkward!) and she said everything looked fine. She said it could be due to the low weight, stress, and the internal problems I was having (the constipation and abdominal pain). If I didn't get a period by the end of December she said she thought maybe we should try a low dose of the birth control pill to bring one on. But my mom had to see her in January and while she was there she told her that I had been diagnosed with Chron's Disease and the obgyn said she was not really concerned about it. Honestly, I'm glad right now while dealing with the pain from the Crohn's that I don't have to deal with period cramps and wearing pads when my bum is uncomfortable enough (I'm too scared of tampons), but I'm also afraid...what if I never get my period again? What if I can't have kids later in life? Is this common..anyone else experience it? Am I getting ahead of myself? All comments welcome, thanks so much!!!

I believe you are not getting your period because your weight is too low. Anyone will stop periods when their weight dips too low, as yours clearly is. When I was a teenager, I went through this anorexic phase and lost my period for two years. Later when I first had major Crohn's issues, my weight was very low and I stopped having periods for many months on end. That said, I went on to have two children. I had no problems getting pregnant at all even with not having a period on several occasions.
Oh, and don't be afraid of tampons. They are waaayyyyy better than wearing pads if you ask me. Less mess and you'll wonder why you didn't start them earlier. Good luck.

Thanks everyone for the replies. My doctors are all aware and don't seem to be concerned..I was just wondering. My weight has always been low and I've never had an eating disorder or any medical problems prior to the Crohn's. And I only just started the Prednisone in the hospital. Maybe I will make another appointment with the obgyn though to talk with her.