Aw, Jenbug, I'm so sorry you are having such a rough time! I replied to your other post in the surgery thread. I had a fistulotomy in late June and I'm doing great. My story is a bit similar to yours. I caught a nasty flu that caused violent diarrhea, which in turn caused a fissure. The worst pain in the world!!!
I had surgery for the fissure in May, which really helped, but as a complication of the surgery, I developed a small abscess, which then developed into a low, superficial fistula.
But, as I said, I had a simple surgery and now everything is sooooooo much better. :D
I definitely understand your frustration! There is nothing like butt pain and very few people understand it. :( I really believe that you should talk to your surgeon. GI docs are great, but they don't always specialize in these kinds of things. Colorectal surgeons (CRSs) deal with fissures and fistulas all the time (these things are actually very common).
Your surgeon is the best person to determine whether what you have is a fistula or scar tissue. If it's a fistula, then surgery is the only way to fix it, as long as the fistula was not caused by an underlying condition, like crohns or ulcerative colitis. (I haven't heard of any effective non-surgical treatment for simple fistulas, I'm sorry to say.) Your surgeon and your GI can give you tests that will rule those conditions out, if they think there are reasons to suspect them.
About 50% of abscesses eventually form fistulas - and there is really no way to know what will make the fistula form, it's really a matter of luck. If your fistula was caused by the abscess from the the food poisoning, and if it is low and superficial (which it probably is), you will likely be told that you need to get a fistulotomy. This is a pretty simple surgery where the doc 'deroofs' the fistula so that the wound can heal from the inside out. It sounds horrifying - I know! I cried loudly when I had to do it. But it wasn't nearly as bad as I thought it would be and it gave me my life back. I have no pain now and I'm living my life again.
I really do understand your pain and frustration. I was there myself not too long ago. Vent here all you want and ask any questions you want. There are lots of great people here who can offer solid advice and wonderful moral support. I hope some of the information I gave helps you. I know this is a scary thing, but there really is hope. You definitely can get your life back!