Why am I bleeding after intercourse?

PLEASE HELP. I started to have sex in October 2010. I have only had it with one person, and it has been multiple times over the past 7 or so months. We don't use a condom too much. We have never had sex with anyone else but each other. The last three times I have had sex I bleed after ward and during. Does anyone know what this could be? Please don't judge, i just need help.