well you could go to the vet and if you look in the pet sections at stores and stuff they have a lot of rub-on medecine for dogs and i think there is also shampoo to help that!
Do you know what it's allergic to? If it's food try and get a hypo-allergenic food. If it's grass....it is alot more complicated my vet told me you need steroids. If you know what it's allergic to i would go to your vet and find out how the best way to treat it is. It could be dust, shampoo several different things that are easy to change and make your dog alot happier. good luck