I haven't started my period yet, and im worried.?

I am sixteen and I have not had sex. My boyfriend and I do other things, but we are very carefull. Three weeks ago we got very active and when I got up my shorts were wet. Could it be me or him, he didn't ejaculate but he pre ejaculated. Is there any way the sperm could have gotten threw both of our shorts and underwear?? Could I just be late or could I be pregnat. I was suppost to start today and I have not. I'm so stressed and worried. HELP!