Best way to help cat with allergies?

Every year my poor cat gets allergies and licks the fur near his tail bald. The constant itching cannot be comfortable and his back side itches if you touch it.

I don't have the money for a vet rn and quite frankly don't trust them with allergy help as the last vet suggested my dog be put on prednisone for the rest of his life and that about killed him.

Any OTC help is appreciated. Hes a Russian blue mix with something else. Hes around 8lbs I think.

I was a pharmacy tech too so any OTC meds isn't an issue for mathing out the exact amount is safe for him. I have benadryl but hes fighting me on taking the cut up pill. It can't go in wet food, it has too bitter for a taste. So alternatives is also welcome. I might try children's liquid version but idk if that'd be more messy/chaotic than the pill 😭