First thing I would do is get him off the hills prescription food as it’s ALL fillers/garbage, that can make allergies even worse and cause way more health issues, my 2 other dogs got kidney disease from the low quality food that was all fillers, just like that food you have your dog on from the vet. Vets don’t get taught on nutrition, just promote their food for $$$$.
I would definitely avoid the allergy pills, steroids, and avoid those from the vet, they do way more harm than good.
One of my dogs she was on apoquel pills from vet for allergies, and she was wearing the cone 24/7 and miserable and uncomfortable, it completely suppressed the immune system, they have no immune system to fight viruses or anything or cancer. One of the side effects is cancer. My dog did in fact get tumours and the vet knew it was from the apoquel and now she was just diagnosed with Bladder Cancer 1 month ago

She has been off the apoquel for over 1 year now BUT the damage was already done. I recommend AVOIDING these allergy, steroids(injections and pills) from the vet, and AVOID the Hills, Royal Canin, Science diet and Purina.
Get him onto a better quality foods.
No chicken which is fairly easy to avoid.
And I give Rusty bovine colostrum powder supplement, give it 30 minutes before you feed him breakfast. Let him lick it out of his dish by itself(no food), it’s absorbed better on a empty stomach.
The bovine colostrum is the best shop for allergies, it’s so helpful for immune system it’s even used in cancer treatments for dogs by holistic vets, and has no known side effects or interactions with anything. If it doesn’t help it doesn’t harm.
Rusty’s allergies are 100% better with the good food and bovine colostrum supplement. I bath him 1 day a week, sometimes 1 day every 2 weeks depending on if the grass is wet outside cause that’s can cause flare ups and irritation.
And you can bath him with Kin+Kind brand,, or 4 legger brand shampoo for dogs. There is anti itch in the Kin Kind brand. The 4 ledgers are really good brand too.
You can use apple cider vinegar to wash his paws too.
Probiotics are good for allergies. Really good for immune system.
He could be allergic to the food your feeding right now. I recommend switching to a better food and helping his immune system.
Even if it’s environmental allergies, diet can make a huge difference.