I feel like I'm getting my period but it ended a week ago?

Posted: 31 Jul 2015 08:44 PM PDT

I had unprotected sex about a week ago and a few days after my period ended. I've been experiencing extreme fatigue, noticeably larger breast with sore nipples and sharp pains in my back and cervix like i'm about to start my period. My period isn't due for another 2-3 weeks, what could this be?