2 months of medication, better worse better and worse

Carl is 1.6 years old, I know he is getting up there but this all started two months/three months ago. He has a consistent wheeze and has been to the vet twice, he has taken a round of Azithromycin with Doxycycline, low dose, then high dose. Carl then took Tylosin and amoxicillin from the breeder his brothers are from. He has taken steroids and pain relief ( not at the same time ). He has also done the nebulizer with albuterol. ( I can not use enrofloxin because of a life threatening allergy I could not handle this medicine)

Every time Carl starts a new med he will show improvement, his energy will rocket and I think he is cured. Then after a week on his the new medication his symptoms all come back in full force, he is wheezing loudly and has no energy. I am currently trying a high dose of Azithromycin and doxy because it worked on his brother, but no luck. He has momentary easier breathing when he does a breathing treatment. I am really becoming so hopeless what to do for Carl, what could this be? Is it that he is missing the wrong medicine, or does Carl have something else wrong with him that we can't see?

Thanks for any advice.