What Does Early Vaginal Bleeding After Unprotected Sex Indicate?

Hi, my period this month was due on the 23rd of December, but I had unprotected sex on the 13th and I started bleeding 7 days earlier than my period (a few days after I had sex). I thought my period had just come early although I was a bit shocked as I never come on early, always a few days later normally. Anyway, the last few days I have noticed that I have been quite sore and having a lot of discharge and a bit of what looks like spotting. I have also had a temperature and bad cramps and am not quite sure what is going on or what I am quite so sore.