Well, I'm dealing with that issue as of recently and I don't know what is behind all that yet. I am getting screened for fistula, even though I don't have all the symptoms that would really relate to that, they are trying to rule that hypothesis out. I'll know about it soon.
So yeah, persistent UTI may be the sign of a bowel to bladder fistula. Usually there would also be fecal matter and/or air too on occasion. If you feel like you have air, that is a very good chance to suggest a fistula.
On the other hand, some people do have a tendency to get repetitive UTI even though they are mostly healthy and often, doctors can't really tell why they do have that. Two friends of mine had that issue, one went to a bunch of specialist to be eventually told to always "overdose" herself with vitamin C. I say overdose but it really isn't since there is no bioaccumulation. The extra vitamin just get rejected via urine and therefore helped preventing reoccurence. She never got a problem after and before being told that tip, she had gone through multiple courses of different antibiotics without success.
So, I believe it worths talking about these UTI with your GI and maybe trying the vitamin C thing could help you aswell (she was told to take 3 instead of 1).