My cat has seasonal and food allergies. My allergies this season are horrible. Narrowing food causes is a long road. Ask your vet about Zyrtec in the meantime. Many food allergies can be chicken, seafood, additives, mites on dry food and a lot more. There is allergy testing were an area of the pet is shaved and like with humans a stick allergy test is done. I would estimate a year to narrow down food allergies then a year seeing also seasonal allergies. If you do any food changes slow and steady. It can be a slow road but rule 1 is kitty must eat. The more limited food isn’t always easy to get them to eat. No matter how good the food they must eat. Changing food does not clear allergies overnight. In the meantime there are meds if this is allergies. I use generic Zyrtec. Clear it with the vet and the dose they recommend.