Hello Bev317 - welcome to the forum. I had Westies for some years but now have Cairns. One of my Westies had skin problems too - thankfully not too severe and this was part of the reason why I changed to Cairns. I'm sorry to hear that your little pal is suffering with this. The problem with scratching is that they can infect the skin which makes it sore and more itchy. I used to find that with a couple of weeks of antibiotics and steroids it settled down. Regarding food, Orijen scores well on the AADF website so I do hope that it helps. The thing about the Westie skin condition is that it is difficult to know whether it is due to allergy or genetic - I rather think it is the latter.
Do you have your Westie clipped or stripped? If it is the former, then make sure that you regularly brush and comb him to get the dead hair out. As you probably know, they are a double coated breed and clipping leaves behind dead hair which, if they are stripped is removed. Use a steel comb - the ones with two sides, fine and wide teeth are useful. This should get some air to the skin which might help. With my Westie I was advised by an experienced breeder to use Selene shampoo and I used to find that this was effective.