I haven't had my period since October 20th?

The first day of my last cycle was October 20, 2010. Today it is November 29 - about 40 days. Throughout all of November, I've been moody and PMSing a lot. I've been bloating and cramping - basically I have the EXACT symptoms I would have like having my period except there's no blood. The first time I ever got my period was October 2007 and I was 12 then. I've had my period for about 3 years now and I'm 15. I weigh 96 lbs. and I'm 5'2. I take Vitamin C, D, and Calcium everyday. I eat regularly, but a couple weeks ago I had a bad cold and didn't eat anything at all - just a cracker a day and ginger ale, plus I was vomiting almost every morning of that week until the cold finally went away during finals week which was right after. I'm pretty sure I lost weight from that and I know that can upset my menstrual cycle, but ever since then I've been eating regularly and have been hungry WAY more often. I'm also craving weird things, but I always do so I guess that's not different :] I told my mom and she said that it's normal and it will come soon. My period hasn't skipped EVER since December of 2007 - I had my period in December 2007 then it skipped January, then I had it in February 2008 again and it never skipped after that. Now it just randomly skipped this month and I'm wondering why? Also, I'm not ually active at all - I'm a virgin - never had a boyfriend,not even kissed a boy before. I know I asked a similar question a while ago but now I'm starting to get concerned. What could be the cause? Anyway, if I don't get it by next week I'm going to see my doctor because as far as I know this isn't the norm for my body...