What Causes Heavy Menstrual Bleeding With Light Colored Tissue Pieces?

I started my period this morning and since 7 am I have had to wear 3-4 pads at a time because I am bleeding so much. And after I pee when I wipe besides the tissue being overly full of blood I am passing tanish pink to light gray colored oatmeal size pieces of something . Never had either of these before. What could it be? I was told by a friend it could be pieces of my uterus lining, is the possible and what do I need to do?