Has anyone else experienced this??

I'm 29, have endo, and was not sexually active since last summer until last night. Had pain immediately after sex, which has been normal in the past with spotting. Had sex last night and this morning (about 10 hours after) had severe pain and a lot of bleeding, like a very heavy period with clotting. It has lessened throughout the day, still having pain. Has anyone else experienced this much bleeding so many hours later? On the pill and STD free.