And this includes the bleeding and the cramping. Now, the final question I want to address is why does the woman feel these pains, the cramping? Well, that's because progesterone doesn't only increase the thickening of that endometrium but it also blocks it inhibits the uterus from contracting. But when the progesterone level drops, that doesn't only cause the deterioration of the corpus lutein and the eventual discharge of the endometrium. It also lifts that inhibition from the uterus. And what that means is the uterus can now contract.