First make sure there is nothing in the environment which may be causing itching.
Check for fleas - perhaps use a topical treatment from your Vet just in case...I don't use any flea treatments long term, but, if the dog is uncomfortable.
Put your dog on an allergy diet for 8 weeks to rule out food intolerances. A good one with few ingredients is Californa Natural by Natura.
Add omega 3 fatty acids into your dogs diet. You can add this with fish body oil supplements. Canned sardines in water, canned wild alaskan salmon, flax oil, crushed flax seeds, hemp oil.
You could also take a nylon sock and fill with oats. pour warm water over it until the oats become sloppy and apply to your dogs irritated skin to help soothe.
Have your dog looked at by a Vet just to get an idea of what's going on.