Uti and more in a dog questions?

Ok. Really don't know where to begin. I got a 9yr 9mo old pit. over a month or so ago, he had a urinary tract infection. I took him in, was put on antibiotics, he got better and returned to normal. We recently went on a vacation and I boarded all 3 of my dogs. When we picked them up, they all looked a little skinnier, which I just thought was because they were in a strange place and maybe were'nt to worried about eating. Anyways, I picked them up on a friday and we all took a nap. The next day I noticed my older one was acting wierd. His spine was showing more. I thought it coulda been from the little weight loss, but, I was worried and took him back on monday. The vet examed him and was more concered with his back because he did squat when his lumbar area was touched. The vet was in a hurry to give him pain meds. I told them to do an xray as well. Xray looked pretty normal except a little spot that showed signs of arthritis. So, for a couple weeks I also thought it was that and went along with the pain meds. No amount of tramadol and rymidal was giving him any relief. I cant stand to see my dog in pain and I called back. Spoke to another vet and he reccommended a cortisone shot. Still no relief. I took him in again, spoke with another vet about what we could do. We did bloodwork. It came back a uti but not showing signs of bacteria. The urine test told more of what was going on. There is alot of proteins and irregular things in that test. Iv'e been racking my brains daily and spending money up the butt on him. I'm now suspecting bladder or kidney stones, or something else? He is urinating, but has a little bit of a hard time and has to go out all the time. He is currently on clavamox and prednisone and seems in less pain, but still very lethargic. I'm gonna take him in for an ultrasound tomarrow or tuesday. I guess my question is, has anyone put their dog through surgery for similar problems? What can I expect? He is almost 10 and already had his tail amputated last april because of a mast cell tumor on his rump. I will spend the money if I knew it would relieve him and make him stick around for a bit. Otherwise, I'll put him to sleep. I really hate to put him down if it's something that can be fixed and improve his quality of live. I'm kinda torn on what to do. I just can't stand to see him the way he is now though. I also wonder if the missed diagnosis has left us running out of time, as I know uti's must be treated quick. Anyone have anything good to say, tips, help, anything? Anyone else go through this? Thanks in advance!Uti and more in a dog questions?
imo if the dog is going often as in constant squatting and if the test shows bacteria etc in the urine sample that you have is a UTI which is easily treatable. imo it could be as you have put possible kidney/bladder stones. this also causes pain because stones are painful to pass. i would go at the last resort in putting down the dog if the treatment doesn't help it and the dog is in constant pain and wont eat/drink etc.