What Causes Vaginal Bleeding After Intercourse?

i'm sorry this is weird, but i have a question. my boyfriend and i have been having sex for over two years now, i am 19. i've never had this problem before except the first time we had sex. Lately, meaning the past times, we get done and i'm somehow bleeding, a lot. i don't know when i start bleeding because i don't feel any pain or discomfort. please help, thanks.