Hurts to sit when I'm on my period

Tianna
Does anybody else experience this? Any pressure on my rectum (I.e. Sitting, washing my backside in the shower) hurts the area around my uterus. Putting a tampon in hurts, having a bowel movement hurts. It's like a tremendous pressure. Only on the heaviest day of my period which is very heavy with clots. Could it be endo?