What Causes Menstrual Cycle With Clumps Of Tissue Discharge?

I'm a female, 26, 125 lbs, 5'6". Always had clear pap smears. Going thru my period and had unusual discharge. It felt like a clumps of possible tissue, but there was no signs of blood on it and it wasn't spongy...I understand this could be my uterin wall, but I have never seen anything like it It's smooth and white and more hard than a soft spongy appearance I would assume the tissue would look like. IS this something i should be concerned about? Not being sure i put it in a plastic bag in case they would want to see it. Just never seen it before...it wouldn't involve a miscarraige, would it?