What Causes Vaginal Bleeding After Intercourse?

Hi, so I've NEVER asked a question like this online before,but



here it goes. Im 18,recently had my FIRST period ever on June



12,2010. It lasted 5 days,which ended on the 17th. I stupidly



had unprotected sex with my boyfriend on the 21st. Then I



starterd bleeding on the 29th. Not too heavy,just enough for



one of those little panty liners. It was at first light pinkish,then



it turned brownish,and then reddish. It only lasted 4 days,with



today the 2nd of July being the last. My next period howver isnt



due until July 12th. What do you think this could be/mean??



please help,THANKS in advance!