I was having the same problem with our two. I switched from Royal Canin to Innova Evo several weeks ago & also just found this shampoo at a great store we have in OKC called "Paws Around Town". The shampoo is called "Bobbi's Itchy Dog" & when I was checking out the owner said it is a great shampoo! I bathed them last Saturday & they do seem to be doing better. She said it is mild enough that you can use it all the time. I bought another kind called "Pet Silk" Tea Tree Oil Shampoo which she said was also good but that once their skin is doing better quit using it. Here is the webside for the "Itchy Dog" shampoo. Hope this helps.
http://www.bobbipanter.com/indexfast2.html