See, thats what Im afraid I will have to go thru too....having to take her back repeatedly and my cat is almost 18yrs old. I just dont think she could go thru all that.
With yours a year old, I would have to think it must be allergies and if you do a search online....which I did.....you will see all kinds of ways to figure out what it could be.
My cat could also very well have allergies, and I have two other cats, who are 2 yrs old, and they dont have a problem at all. My house seems to be extra dusty and I have to wonder if that's it. I just dont think she will last much longer being so old and Im not sure that I could even solve this problem in time.
Hope your cat gets better!!!