Help me?!

Okay so my period just ended 2 days ago and my discharge is totally abnormal! The color is very dark yellow, almost a brown and has a terrible odor along with more of it than usual. My cramps still haven't stopped either. I don't know if this has anything to do with it but I was getting extremely hot and sweaty in class for no reason at all and my stomach was hurting SO BAD the second I would move and as I would keep moving it would get worse but it was off and on. I felt like I was going to throw up any second! Now that I think about it I may have kept a tampon in a little too long.. What do I do?! I'm 15 and not sexually active at all.