Same problem i faced with my GSD when it is 3 months old. Its very hard to cure it. i used to go to vet every day and 3 injections were given a day. Its not expensive but lots of care should be taken. First take him to doctor. Use Venkeys Keen & Sheen shampoo (every 3 days) that will clear allergy , after this rub with towel the skin leaves lots of dust in white, remove it. Apply kis kin lotion 3 times a day for the whole body.It will take up to 15 days. During this process u should observe its legs. Bcoz due to weakness its legs beds at its paws. All this can be done only after giving it injections for drying up skin disease.