What Causes Dark Brown Discharge After Having Unsafe Sex?

I had my normal period at the beginning of the month like usual it ended on the 14th, my boyfriend and I had unprotected sex at about 6:00am the 22nd, later that day I had a brownish red mix of blood and discharge and it has continued on to today the 23rd, but now it is just dark brown no red. I have never had this happen before what does it mean?