Hi , my name is Monica, and i have a Dozer too, he's 9 months old. I was going to mention all of the above reasons that you already mentioned, UTI, stones, etc, but since these have all been ruled out, I'm stumped for any other reasons. I just wanted to send my love, thoughts and prayers your way , and hope that it clears up. You are doing everything you can, by taking Dozer to the vet, the antibiotics, the googling to see what it could be , and following up with the vet again. Hopefully it clears up, or the vet can figure out what the cause is. Keep us posted on Dozer and let us know how he's doing. Good luck and hope all is well.