Honey is high in sugar, and will attract and feed certain bacteria. It does fight certain other bacteria, but probably not the ones that attack the bladder. Because you're on antibiotics, the Kefir probably won't hurt, but you'll get more value out of a good probiotic supplement. The reason for this is that the antibiotics will kill off the few bacteria in the kefir, and the dairy might attract the bacteria, while a probiotic supplement has billions of organisms in it.