Karen is correct - two doses of Clavamox is not enough to fix a potential UTI. We normally prescribe it for 7-10 days. Taking antibiotics sporadically and not for the full length of time they are needed to be taken can end up causing bacteria to become resistant.

Have they taken X-rays? Since the antibiotics originally prescribed didn't seem to fix the problem, it could just be a very persistant UTI, or it could be bladder stones.

Another very small possibility, since you say he is intact, is an issue with his prostate.

In any case, the ONLY solution to your problem is another visit to the vet. I understand money may be tight, but a UTI can be VERY uncomfortable for your pet. Maybe call your vet and explain your situation; some vets will accept payments if you're a client in good standing with the clinic. There is also the option of care credit too.

Good luck, and please keep us posted.