What Causes Spotting, Stomach And Back Pain After Intercourse?

I had sex with my boyfriend on the 21 of july 2010 a week later i was having sharp pains on my side and lower stomach...also i was had some sharp pain in my breast..in july my period came on early..which was july 7 2010 and my period suppose to come on the 8th of every month..anyway this period was normal..i only spotted for 4 days..and now its august 5 and im spotting again and im having really bad pain in my lower stomach and lower back.can you tell me what wrong with me