Hmmm...maybe ask for an x ray? My older dog gets periodic UTI's, they are caused when she gets a build of bladder stones. It's relatively cheap to get her X Rayed (I want to say it's less than $50) and helps us head off the infection by spotting and removing the stones before they become an issue. We also switched her to filtered water (we bought a filter thingy for our kitchen tap) and that has actually stopped the stones from reappearing *so far*. Of course your case could be very different.