I have a supra pubic catheter and have constant uti's that have bowel bacteria in them. ileostomy as well. could i have fistula small bowel - bladder

Possibly: Urinary tract infections commonly have bowel bacteria, but if you are concerned and you keep getting them soon after finishing antibiotics it is worth having some testing to determine if there is a fistula. May involve a ct, a cystoscopy, or a dye study. Knowing more about why you have an ostomy and a suprapubic catch would allow a better answer.

Fistula: If u have a fistula between ileum and bladder , you will have some faecal matter in the urine as well along with uti. It is serious condition . If it's just uti , unlikely to be a fistula. Discuss with your surgeon please.