Hi Meghan, So, of course any time you are having sex, there is the risk of pregnancy, and not all women show symptoms in the beginning, that's why some women or girls when they do find out they are pregnant & have their first ultrasound, are 8 or 10 weeks along. However, there are other reasons for delayed periods, you are only 17 & mentioned that your cycle is not regular to begin with, so this could be a time when your cycle is off. Stress is a big factor in missed periods for women, if you are stressed in school, or at home, in your relationships, or just with life in general, this can cause you to miss your period. I would take a home pregnancy test to determine whether or not you are pregnant, if it is negative, wait two weeks to see if you start, if not then I would talk to your mom about getting you in for a pap smear to make sure there is not another reason for your delayed cycle. If you are pregnant, you have to talk to an adult you trust, friend's mom, school nurse, school counselor, about your options. I hope this helped, Good luck to you! I'm on here all the time if you need someone to talk to, no matter what the results are ok.
my grandmother said the same thing to me after i told her i did some thing i wasn't suppose to do.