I wouldn't give your dog steroids, they work by shutting down the immune system in order to do what they need to do. What you want to do is let his system heal and his immune system strengthen. You could also give him a probiotic, this will encourage healthy gut flora and keep his insides happy which makes the outside happy.
Has the itching only been an issue since the fleas. If you can find a natural shampoo without oatmeal, give him a bath in that. Run the flea comb over him a few times check around the tail and bum and groin as well as the neck and head. The little buggers like the warm bits.
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