It may be more than just a flea allergy. What are you feeding Tobie? It might be something in his food or a sensitivity to something in the environment. Regardless, allergies are a tricky thing and it's not too surprising to need multiple visits to the vet to pinpoint the trouble. Might not be a bad idea to have a scraping done, too, to rule out things like mange.
Good luck, Tobie!! Hope you're more comfortable soon!