More allergy sources can include detergents not being rinsed out of bedding, carpet shampoo residue, or other household cleaners.
How is the flea control in your household (or any other place you take your dog) as it can take a single flea bite to set off a reaction in a sensitive pet.
A very overlooked source is exposure to smoke as it's a skin irritant as well as damaging to the lungs.
FYI - Temeril is prednisone and long-term use isn't reccomended.