My 15 year old boy is very itchy and has been doing the flea gnaw. But I took him to the vet and the vet said there were no fleas. They gave me predisalone to help with the itching - doesn’t seem to help.

He’s only losing hair around his rump, but he’s itching in the classic flea spots (neck, belly, rump). The only other thing i could think of is we had gotten one of those bed bath andbeyond air freshners, realized how bad they are for pets about two weeks later and unplugged it. We washed the walls in the room the air freshner was in and shampooed all the carpets. I tried giving him an oatmeal bath and that seemed to help for a day or two. Any hypothesis? The next step is going to a cat dermatologist and that is likely going to be so so expensive and i feel like the vets pretty much guess and check themselves. Not looking for medical advice so much as im seeking similar experiences. Has this happened for anybody else? What did you do/what did it turn out to be?