Wtf. I don't know what just happened.

So my period came 5 days ago. The first 3 days was brown discharge, old blood or whatever fine. 3rd day finally had bleeding. Nothing serious. Had to change pad every couple hours. Today (5th day) was light all day, I worked for 6 hours running around and doing a lot of moving. Yet nothing crazy came out of my uterus,just a little blood. Now I just happen to go to check/pee at the store and I had to leave because it was a fu*king crime scene. My underwear was soaked along with the pad and my pants were getting to that point. So wtf is going on? It doesn't do this. It just doesn't randomly get heavy like that.