What Causes Nausea And Spotting After Intercourse?

I had my period and maybe three days later I had unprotected sex with my long-time boyfriend. Two days later I started bleeding again. It started out as just small spotting that I noticed when I wiped but now it's bright red small dripping spots. I have an IUD. I have been feeling a little nauseous but I don't know if it's because of the holiday celebration that I was doing. I'm nervous.