Three months late, not pregnant. What could be wrong.

Patient: I don’t really know where to put this, because it’s not related to pregnancy. But, I’m 18, I’m 3 months late, and I know I’m not pregnant because I’ve never had sex before, Or been with a guy for that matter. I’ve been reading online as to why I am late and some of the reason could be that I may be stressed, gained or loss weight and other stuff.I haven’t gained or lost weight, and I’m not over weight. I don’t think I am. 133 5’3″, you tell me, I don’t know, but I’ve been this weight for like a year and never had it as a problem.I can say that for the first month, I was stressed out, a lot. Because I was moving from Florida to Utah, 5 day drive to there, and I was stressing all the way up there. So, I can understand why I would miss a month. But, the other two months are beyond me. So, if you have any idea of what could possibly be wrong, tell me. Thank you