I'm 18 y/o. my cycle is usually around 32-34 days. had 5 minutes sex w/my bf 3 days before period is due. now i'm a day late. will i get pregnant?

Probably not: Typically ovulation occurs about 14 days before menses begins, but there can be variations. If you don't want to be pregnant you should use appropriate contraception and never have unprotected intercourse. Do an ept; if negative repeat it in a week if you don't start your period.

Presuming that your: menstrual cycle is routine, you would ovulate at roughly day 14-15. The unfertilized egg dies within 24 hours. That said, sperm live in the female's reproductive tract for up to 10 days. With respect to your last sexual encounter, statistically, you would have no viable egg to fertilize. Earlier unprotected sex, from roughly day 5-15+ would potentially cause a pregnancy. It's all in the timing.