Uh.... women only pleeeeeeezzzz....?

I was supposed to have my visit from aunt flo like... a week ago. I never got it! I can't possibly be pregnant, I've never had a boyfriend or like any real romantic relations with a guy.... so that possibilty is like out the window. I'm also on accutane, I don't know if that has anything to do with it... I'm 17, and I've been pretty regular for a very long time. But now? Geez, anybody else ever have this problem? I had some cramps last week and one this morning, but like... what gives?