Dear, Chris
Sweetie most likely you are not pregnant. On an average 28 day mensual cycle you are fertile around 14 days after the first day of your last monthly period. If sperm is present when you ovulate then fertilization can take place, once the egg is fertilized it takes 7 to 12 days to travel down the fallopian tube and implant in the uterus lining. When implantation occurs it can cause some spotting which is around when your period is due, most women mistake implantation for the starting of their menstrual period. The first day of your missed period is when you can take a pregnancy test which is around 14 days after you ovulate. Since you had sex right before your period you most likely were not fertile. I recomend all sexually active girls to go on birth control for added safety against pregnancy. Stay Safe
Love, Falon