[anonymous]

Call the vet and ask him to return your call when he has a minute. Direct your medication question to him.
Discuss what other flea/tick preventives would be appropriate for your pet.
I have one dog that had a localized reaction to a topical (Advantix), mild rash exactly where I applied the topical, no pruritus or other symptoms.
For that dog I am using the Seresto collar, so far it’s working. Years ago I had another dog that developed a rash due to a tick collar, my other dogs had no problem with it.
Every dog is different, and as you have found out, the natural stuff doesn’t work.

As far as medicating with over the counter meds (not intended for veterinary use), I think you should ask your vet, I don’t know your dog’s medical history, age etc.
It depends on how bad the pruritus is, you may want the vet to examine him first…..he may need a shot (immediate relief) if it’s a true allergic reaction.

The Benadryl dose is usually 1mg to 1 pound of dog, example 25 mg for a 25 pound dog, the pills are scored and can be broken in half. Do not use the children’s liquid it contains ingredients that are contraindicated for dogs.
Benadryl at it’s best is mild and often not very effective. If the dog is as uncomfortable as you suggest, I would take her to the vet for a shot.

This is not veterinary advice; consult your veterinarian.

Ps: If the dog is red all over, rash on the chest, difficulty breathing or any other concerning symptoms, I would go to the emergency vet, NOW.