What Causes Brown Vaginal Discharge?

I've been on this medicine called spironolactone. It's for treating facial growth due to POS. I started my period two weeks ago 6 days before I was suppose to start. This isn't normal for me bc I am usually irregular with periods being a week and a half to two weeks late. But I figured it is the side effect of the medicine I am taking. I then had unprotected sex a week ago but he pulled out way before he finished. Now 7 days later, I get this brown discharge and felt like a period. Is this due to my medicine I am taking? It's too soon to have another period since I just had my period two weeks ago.