I had a fistulotomy before I was diagnosed with Crohn's, for a fistula. Let me tell you mine did not want to heal either. It stayed
open for a solid year before it finally closed up. It was awful, but at least at that point it didn't hurt. But yes, once I found out I had Crohn's it explained why it took so long to heal up. My surgeon was fine with my slow healing, just kept checking on it here and there to make sure nothing was infected. I haven't had anymore problems since.
Good luck with the Remicade. The cancer risks scares me with those drugs (Lymphoma is in my family).