? URI or allergies

I was wondering if anyone on here has expierence with URI, or allergiesi? Bubby has had these issues reoccurring since his first visit to the vet in early February at which time they thought he had asthma and gave him a steroid shot. That shot which they believe triggered the diabetes because prior to that his blood test were excellent. He will have sneezing, snorting, swallowing, shaking head, and watery eyes and sometimes nose. He was treated with azithromycin which helped for a bit. We thought our two cats were trading it back and forth but his never totally goes away. When he was hospitalized for the diabetes and pancreatitis they said he showed no signs of it. As soon as we brought him home he began shaking his head and sneezing again. After a few days it seemed to get better. Just in time for a trip to the vet at which time it came back worse than before. Now he even has an occasional cough. They think he may have asthma too but when he coughs he doesn't even bother to stand up sometimes. He now has an inhaler with albuterol. He is sleeping a lot the last couple of days then SURPRISE, this morning he was bright eyed and upbeat not sounding congested for a few hours then after his miss day nap all symptoms are back. I'm so confused and my heart breaks cuz I don't know how to help him feel better. We are running a humidifier and just started lysine. Are these ups and downs and lower immune system anything to do with the diabetes which is still unregulated (we were planning to do his first curve this weekend) at his vet visit Wednesday they did blood work and chest X-rays and said things were getting better.