You say you've had many tests, just wondering what one's for the bowel?
Colonoscopy ? Bowel series ? Sigmoidoscopy? there are so many different tests so you still might have some options..

I too had endo which has disappeared for now and gives me no trouble, but I suffered awful pain as you describe through the bowel when I did have it, best to make an appointment with a Gyneoncologist if you haven't seen one yet

Hope you feel better soon