I'm so sorry you're having so many issues, and to top it off you're sensitive to most of the ostomy products, sometimes you just can't win, sigh.
I think you would have shown signs of Crohn's if you had it, and hopefully your doctor would have picked up on it. Diarrhea, stomach pains, constipation (yes sometimes D sometimes C), elevated WBC, elevated C diff, blood in stool, mucousy stool, and list could go on and on because it's different for everyone.
Unfortunately, unless you have a disease (which truthfully I don't know of any others besides CD) that's likely to cause fistulas, medications probably won't help you and surgery is your only recourse. Even if you do have CD, medications don't help all patients, and surgery is sometimes necessary (like for me).
Of course, medicine is an inexact science so anything is possible. There is a new test that shows a high percentage of accuracy for diagnosing Crohn's disease and/or Ulcerative colitis and it's made by Prometheus. And there's always the possibility that you could have this disease (I really hope not for your sake) and not have any symptoms yet.
I hope you can find a solution that not only gets rid of your fistula, but will also make your life easier. Good luck and keep us posted.