I came across a this post that provides information about how to help your itchy dog. It suggests daily bathing.
I have been dealing with my dogs itchy skin since we was about 2 years old. He’s now 6. I have tried numerous things over the years – changing diet, topical treatments, food additives, a treatment called Nzymes- all without noticeable results. In fact, as I type, my dog is scratching his little heart out. It bothers me that he is so uncomfortable. My own experience has shown that my dog always feels better just after a bath but that the itching seems to get even worse a week or so after a bath, which is where he’s at right now. He has sores on his legs and on his abdomen from chewing and rubs against you so you’ll scratch his back. Perhaps the answer is in more frequent bathing as suggested in the post. I can see this would be a major inconvenience, though a relatively inexpensive treatment. Worth a try.