Definitely sounds like a fistula. I have one and it isn't fun! I've been dealing with mine since Oct. 2010. I have had to take massive antibiotics and have had surgery twice to place setons, and one FLAP surgery that didn't work. I'm hoping to have another procedure next year and my c/r surgeon is bringing in a pelvic reconstruction specialist.
Try to get a referral to see a c/r surgeon. My GI was no help (still isn't).
Hang in there.