Some of us saw your post earlier today and responded to you. Scroll down and read what we had to say. I would not worry if I were you, though. Tell you parent(s), relax, and make a doctor's appointment. It's probebly nothing major. Like one of the other ladies said, you are young and, I imagine, just starting out with your period. It might not be regular yet.
Oh hunny I'm sorry for your worry! Listen, when I was your age (I'm 23 now), I would skip sometimes 6 months or more of my period. Stress can put it off!! When I went to college I didn't get it for a year, and I wasn't pregnant. You can't be pregnant if you didn't have sex. If you are worried, tell your parents and they could take you to a doc. But it's totally normal!