If by some chance you are pregnant, it could be by pre-cum (I don't know the technical term, sorry) or maybe it's just your nerves. Sometimes stress can cause you to miss your period. The best thing to do right now is to buy a pregnancy test. If it comes up negative, buy a couple of more just in case because pregnancy tests normally only botch when you have a negative result. If it comes up positive on your any of the tests you take, then schedule an appointment with your gynochologist.

 Hope I helped.