What Could Foul Smelling Discharge During Menses Suggest?

I am 16 years old, around 5'6", 125 pounds, and am normally pretty healthy. My period is in it's last discharge day and you can't smell it from far away, but if you smell the discharge it smells like rotting fish. It's pretty thin and has a orange tint to it. It almost immediately will form a film on your finger and it is shiny. Also, tampons are making me sore this time and they usually don't. This isn't normal. What could be causing this?