my dog has bumps all over him,vet thought it was bee stings and benadryl works for about an hour?

Could be anything. Maybe flea bite dermatitis, some animals are allergic to flea bites and they break out. The bite from just one flea could make him miserable. Could also be a food allergy. There are foods with limited ingredients you could try to see if that clears his skin up. Also a bath with either an oatmeal shampoo or a hydrocortisone shampoo may bring some relief.

Perhaps you should take your dog to see a different vet, especially if what your vet said and told you to do isn't working. Honestly, that doesn't sound like a very good vet to me, if they 'thought' it was beestings and doesn't really know. I'm sure there are ways to tell what it is.