I had a post surgery fistula in my abdomen. I had it for 2 years attempting to heal with with meds but it wouldn't. It took 2 surgeries to get it to close completely, and even then my surgeon left me with an
open wound incase it started draining again. So it took about
6 months AFTER surgery for the wound to actually completely heal up.
I didn't really have pain from it, but what did hurt was how irrirated it would get from the drainage, UGH I wouldn't wish that on my worst enemy. I used baby wipes to keep it clean, and I changed the banages about 5 times a day to avoid drainage bothering my skin. My GI said it was OK for me to take baths, so soaking in the tub helped a lot. I have heard many people say that their doctors told them not to soak it so I would ask before doing it. Sometimes I used diaper rash cream around the opening. There were nights that I just wrapped a towel around my stomach and slept because my skin was soo sore.
Fistulas seem to drain worse when you are having D, so I would avoid fatty foods and such, eat plain rice, breads, pasta...