Lately when my bf and i have sex a day or two later i bleed i already passed my period so why does this happen?

Spotting: Even though it's not your period, vaginal bleeding like this can be caused by fibriods, endometriosis, dysfunctional uterine bleeding, or even pelvic inflammatory disease. Usually your doc will take a complete history, do a pelvic exam, and will consider an ultrasound. Treatment, like most things, depends on the cause of the bleeding. A pregnancy test is the first step. Best of luck.