The Life's Abundance is great for those with allergies since it has no corn, wheat or soy. It is all healthy ingredients too.
There is a skin and coat supplement that is fabulous for allergies and the itchy skin. It has the Omega-3 Fatty Acids/fish oil in it.
If you want to try a sample of the dog food, just PM me.
Check the ingredients on the food that you are feeding now. The fish oil should help but probably cannot counter act the dog food if it has the corn or wheat in there.
You will want to use a good shampoo too. The Spa Scents Pet Shampoo is wonderful for yorkie hair since it doesn't strip out the essential oils that are needed to keep their hair silky and their skin soft. If you use a harsh shampoo, that can dry out their skin too much and cause itching.
Hope that helps.