What Causes Vaginal Bleeding After Intercourse?

I got my period October 9th, 2010 and it should have been over by October 13th, 2010. Well two nights ago I thought it was done, so I had sex. Then I wake up the next morning and there is no blood but when I go to the bathroom thirty minutes later there is blood. Then today I took a shower because I woke up with blood again and after my shower there was no blood but then about an hour later there was, but only a little. I have no clue what to do and I can't go to the doctors office because I still live with my mom and if she would find out I've been having sex she would get really mad. I need help please.