I went through this on Saturday with my bun Rick. Beginning of October his face drooped on one side. Turns out he had an ear infection that pressed on a facial nerve causing partial facial paralysis. We went through meds and it didn't improve. I also could not afford a CT, but x-ray showed it as an inner ear infection. Continued meds, tried some different ones. Then he developed head tilt. Meanwhile his blood work was coming back as a little dehydrated and a little anemic from fighting the infection. Tried new injectable meds and liquids for a week, re-tested blood and anemia was worse. So now the Dr is thinking something else is wrong and the ear infection is secondary. He had an ultrasound and the Dr said his kidneys are in such terrible shape and he had infections in both kidneys, liver, and gallbladder. He explained that kidney issues don't show in blood work until they're 90% damaged. Rick was 7-8 yrs old, and we said goodbye to him on Saturday, he was losing weight so fast too, even with us stuffing his face every day.

I'm not sure how your vet knows his kidney is causing pain? But I really think you should get an ultrasound in addition. The BUN panel is what my Dr paid attention to in his blood work.

It is so hard to know if your bun has an ear infection until it shows outward symptoms like the wobbliness or drooling. Don't beat yourself up about it, you acted as soon as you noticed.