Check with vet, or even pharmacist. He may recommend a child's dose of benadryl to help ease the suffering from allergies. Never give adult dose intended for humans, so check with pharmacist. Many can assist even though they are not vets and can recommend something over the counter you can give to your dog. As well, if his allergies are severe, you may have to get shots for him from you vet. Try the first and if this fails, see vet
Your dog needs to be seen by a veterinarian for evaluation and treatment. I would not rely on the recommendations of a pharmacist in treating a dog, or any animal. Regular pharmacists are "people" pharmacists and their training in ENTIRELY in the use of drugs in humans. Just as you wouldn't give your dog chocolate because of the greatly differing effect on dogs, a "child's dose of benadryl" may be ill-advised in a dog.
My dog has hives and fever