I have had recurrent ones since I was in the 1st grade. They could never tell me why I had them. I was also on a preventitive antibiotic for one year (yes, a full year). It helped a lot. When I got pregnant, they came back and so I was on another one for the duration. During my delivery, I was catheterized for the whole thing. I think the catheter might have dilated the urethra and I didn't get one for 6 months (was I one happy girl). I have since gotten one and seen a naturopath. Her advice: stick with cranberry or blueberry juice, not pills, wash nether regions often, especially AFTER sex and bowel movement; drink water and juice and nothing else (I do tea too); get a sitz bottle and rinse the area after urinating; and finally, eat a balanced diet without much sugar as the sugar is excreted in urine and provides plenty of "food" for e.coli, the most often offender. Wipe front to back, always wear cotton undies, give it an air-out often. That sort of stuff. I had to cut out sugar recently and have found, to my pleasure, that it worked. I haven't had anything in a year or more now.
Also, the chamois has once irritated the area and I thought I had one. But after drinking LOTS and peeing often that day, it went away. First few pees, not so great. Hope it helps!
Mistie