I have had to take our cat to the vet for several weeks.she has had several cortisone shots and prednisone prescriptions.she sratches and her ears get that brown discharge like ear mites,but its not.the vet thought it might be food,so we changed food.then changed bowls.I am wondering if its the cat litter.has anyone had a cat allergic to the litter? She also has very reddish skin all over.