What Causes Brown Vaginal Discharge After Having Unprotected Sex?

I had unprotected sex on day 14 of my 28 day cycle. The day before my period was due, I had what I thought was my period a day early but it only lasted 2 days (usually 5 days) and the entire 2 days it was brown and much lighter than usual. I had pregnancy symptoms right after I had unprotected sex but now I have no symptoms. Could I actually be pregnant or is my mind & body playing tricks on me?