Allergies

What do you guys do for allergies? My basset is suffering pretty bad. I noticed he has accidents in the house A LOT when his allergies are acting up. We’ve tried a few different food brands and they’ve all caused him to itch a lot. And now this new food we’ve been on, he’s been good on it for about 2 months but all of a sudden his allergies seem way worse. His ears are raw and itchy, his eyes are red, his armpits are red, he’s irritable. Idk if it’s food allergies or seasonal or a mix of both. He’s constantly barking and whining because of it. For food allergies the vet always told us to just start taking ingredients out of his food to narrow it down to see what he’s allergic too, but that gets expensive because you’d have to buy a new bag constantly to keep trying. And for seasonal allergies- I don’t want to keep him high off benedryl. Can the vet help with both? Probiotics? Idk where to even start