My Cat has been sick for several months

Question
My Cat is 7 years old (tabby).  Healthy other than 2 previous upper respitory infections at 1 year old and 3 year old.  Recently we adopted 2 great danes and changed the cat litter to pine pellets.  The cat developed sneezing, almost 100 times a day.  I have taken him to the vet about 6 times in the past 3 months.  He was put on oral anti biotics and Enisyl-F paste.  He developed bad diarrhea. He was finished the antibiotics and I just stopped giving him the Enisyl-F paste.  He was treated with FortiFlora and Pro-Pectalin.  The Sneezing is still present and everytime we are at the Vet our cat doesn't sneeze. There is yellow snot present.  The Vet told us to change the cat litter which we have and also warned us about perfume, air fresheners etc.  He said last resort is xray.  Do you think this is the time to insist xray?

Answer
I would follow your vets advice and get rid of the pine pellets, and put the dogs outside. If anyone smokes there should be no smoking anywhere near this cat.

The fact that he had two upper respiratory infections shows that he has weak lungs.
The fact that the cat doesn't sneeze at the vets tells you two things:
One- he is away from the allergen at home and
two- they are too distracted and scared to sneeze at the vets.

But a cat with really severe problems wouldn't be able to stop itself.

So get rid of the offensive items including any new rugs you might have-throw rugs, comforters etc. Even new curtains have compounds in them that can cause this.

Xrays of what? His nasal passages maybe yes- but try the above first. Give that a week or two then go for the xray.