Constipation -ten years post-full gastrectomy...

I had a duodenal switch ten years ago. Had massive complications: Leak; Empyema; Thorocotomy; coma, x2 mo's;
Which ended in a full gastrectomy, colostomy, then colostomy reversal.

I was doing well until about two years ago. I gained 40 lbs, and have severe constipation. No amount
of Docusate, Biscodyl, Psyllium Husk, or mineral oil helps anymore. I am having to use an enema almost every day
or wind up with horrible abdominal pain, sobbing in the bathroom, trying to void...

My IM Dr. Has not helped... Any ideas on how to fix this? I drink at least 120 ounces of water each day...
So i know that cant be the problem. I have been on Methadone for 8 years. Since this awful constipation started,
I have more-than-halfed my dosage, because Narco's can cause constipation... any ideas on how to fix this?

I know my situation is pretty extreme...anyone else have this too?