Please help.. really need advice..

What are the chances of getting pregnant after 4 hours of sex, using 7 different condoms and checking them all before we used them, and making sure no cum got anywhere near my vagina? My boyfriend and I are worried sick and we're just teenagers. His parents would kick him out and mine wouldn't let me see him anymore.. I'm predicted to have my period today and I've had the cramps and PMS of it but still haven't started..