I know that you're scared, but a delayed period is fairly normal. Some girls even skip their periods for a month at a time due to temporary cysts that grow on the ovaries. Just as an example of why your period might be delayed.
Pregnancy tests are cheap and easy. I think that you can take a test just to be safe, and then see your gynecologist after 1-2 months of tracking your period for any irregularity. A constant irregular period can indicate other problems, so track your period on a calendar...and don't worry too much! When did you have unprotected vaginal penetration?