I just thought I'd ask - although I'm sure you've been told: did your doctor go over the other ways to avoid UTIs? (Like I said, I'm sure if this has been a long term problem, they've discussed it with you, but I've worked in health care, and it's amazing what things get missed sometimes! Everyone assumes that someone else discussed it.) Anyways, here are some that I know of off the top of my head: drink lots of water, never "hold it" when you think you have to go, cut back on the caffeine, try the cranberry juice (in moderation), always wipe from front to back, and ALWAYS go to the bathroom after BD.
Hope you can find something to help - they sure are miserable! All the best!