A male friend went through recurring UTIs after prostate cancer. [The implantation of bead markers for the external beam radiation led to the UTI cycle.]
He'd gone through multiple halfway-effective antibiotics for 3 years until a new urologist told him to take D-Mannose daily. It's basically a concentrate of the d-mannose from cranberries and it worked from the second day.

D-mannose makes the soft tissue urethra lining less hospitable for the bacteria so it doesn't stick to the urethral lining. Three urologists and years of UTIs and one visit to the ER for pink/reddish urine and the saga stopped with a few days of taking OTC d-mannose. It this case, he bought the stuff from Whole Foods it's readily available elsewhere. The doctor didn't prescribe any dosage, just said to take amount recommended on the label BUT double it for the first five days or so. Also drink a lot of water to flush out any backed-up bacteria.