Curious

So this has never happened to me before so it's just kinda freaking me out. I got off my period on Wednesday, today is Saturday.. and since I have gotten off my period I have had very light spotting, brown, but today I'm having cramps along this. My SO and I had unprotected sex a week ago today. I've read a few things it could be.. but I was just wondering if any of you have experienced this? Thanks so much