For all you vets or vet tech's out there...?

My dog has been taking antibiotics for over a month now to try and resolve a severe bladder infection. He was first put on Amoxicillin for 2 weeks, during this time he became quite lethargic and developed swollen lymph nodes and a runny nose. After the prescription was finished he seemed to return back to his normal self again. However, whn we took him back to the vet to see how his UTI was doing, we were told the infection was still there. We were given a sulfa drug to administer for another 2 weeks 2x daily. Our dog started acting lethargic again and continued to get swollen lymph nodes in his neck and sometimes under his armpits. When this prescription was finished, he seemed to regain his zest, so we went back to see if the UTI was gone, but it had still persisted with a few sparse bacteria and crystals in his urine, so we were given another 2 week course of the same drug to be given the same way. I have just connected the sulfa with the swollen lymph nodes. What do you thin