What Causes White Discharge In Periods?

Hi I had my period a week ago and all of a sudden I had this really heavy white discharge almost like wet toilet paper coming out of me with a little bit of blood in it? I don't have bad itching it's just a little sensitive and an itch here and there. What could this be. It never happened to me. When I put my finger up there the first day it happened I could pull out a dim size?