What Causes Bleeding After Intercourse?

hi, i am really worried about the possibility of being pregnant. I am 23 and i currently take birth control. i ended my pack for the month, however, the last day my boyfriend and i had sex and i bleed. It was not a continous flow of blood, only during intercourse. 3 days after i was concerned and took the morning after pill. it has been 4 days since and i still have not gotten my period. i don't know what is going on!?