Cramps and brown discharge?

I have been on the pill for a month and a half now. Before I started the pill I took a plan B pill and got brown discharge that continued through my period to the first period I had on the pill. Yesterday, I started getting light brown discharge again and today I am having light cramps. I still have 10 days until my period is supposed to come. I had unprotected sex on Valentine's Day (5 days ago). I don't know if that matters or not. Anybody have an idea what's going on?