I haven't had a period in six months. I'm not on birth control or sexually active with men. I'm 22 years old and have never had this problem before, my cycle was so predictable that I knew what time it would start and end. In September I missed my cycle, I thought it was stress, it came late the next month, then didn't come again until early December. I don't know what to think. Any advise would be helpful. Thank you.