I'm Late!

Help, I haven't had my period since early February! I'm abstinent, so I know that's not the problem. I got a huge assignment in February. I also have been eating more and lifting weights. I work out 4 times a week. My athletic friends say it's normal and I've skipped periods before, but never this long! I've always been a worrier and I'm stressing big time over finals, and this doesn't help. I'm really worried something is wrong with me. Any comments are greatly appreciated! My sister has had a syst on her ovaries and my grandmother had her uterus taken out so I'm not sure if it is an internal genetic problem. But I am DEFINITELY experiencing PMS lol.