What Causes Pain And Burning Sensation In Vagina During Intercourse?

Me and my boyfriend are very sexually active, yesterday we had sex twice. The second time, when he was trying to enter it was very painful and had a burning sensation, the pain did not stop through out intercourse. This did not happen the previous time. When we were done having intercourse, i was having pain around the vaginal area. it has not stopped hurting, now a day later. I've looked at it and its swollen around my hole and puffy. I am on and have been on depo for 3 years, i do not get periods but occasionally get spotting. i was spotting when we were having intercourse, i don't know if that matters.