cats having allergies?!

Skylar
My cat is constantly sneezing, has a little bit of eye dranage, and also is balding on his ears. Inside his ears is this black stuff that the vet just told us to clean out with alcohol. She informed us he has allergies and gave him a shot but that's about it. I feel bad for the dude he seems miserable. What can cats be allergic to? Remedies?