I just went through the same thing with our shih tzu and it was allergies. The vet gave him meds and he doesn't lick his feet anymore. Now he scratches his ears and I KNOW they aren't infected or anything because the vet just saw him. I think he's bored - unless he got something between going to the vet and coming home.
Maybe he still "blames" Jaybay for suggesting he go to the vet = )
If your vet hasn't seen this condition since the beginning, then it's time for a return visit. You're probably right that it's allergy related, but your vet can give you better meds than benadryl to treat it.
Another consideration would be a fungal infection. Doggy athlete's foot is pretty common, and moreso in the summer months. It's irritating, so the dog licks his paws. The more he licks and keeps his feet damp, the better the environmet is to keep the fungus growing.
If you smell his paws, do they seem a lot smellier than the rest of his body? If a fungal/ yeast infection gets firmly entrenched, the dog's bedding or favorite areas of carpet will be noticeably stinky. Most fungal infections can be easily remedied, but you'll need your vet to make the diagnosis and get the correct medication for it.