My boy too has been scratching until bleeding and nibbling, licking legs and feet until they were raw, the licking has also discoloured his leg hair. I was giving antihistamine which helped but didn't want to keep giving it.
This stuff has worked wonders
https://www.amazon.co.uk/supplement-treatment-scratching-healthier-digestion/dp/B00QKQ9YF0/ref=sr_1_26?ie=UTF8&qid=1474750837&sr=8-26&keywords=Dog+itchy he stopped scratching within the week. I then also started giving him lintbells itchy dog formula to help his skin, it has salmon, fish, starflower, and golden flax oils plus vit E.
On both he is fine. The licking has stopped I can see white fur growing where he'd previously nibbled himself bald.
I discovered a while ago that having beef as main protein made him itch. This summer I've also stopped all beef treats such as dried heart, pizzles, dried tripe. I'll try introducing those again to see how he goes.