I've just joined the Pets.ca and would like to give two suggestions regarding the skin problems mentioned.
First, when my dog was a puppy he also had similar sounding problems. The worst being that he chewed himself bloody. We did similar treatments that everyone has mentioned. Nothing worked. I decided to give him Brewer's Yeast tablets and I believe they may have helped. Either these tablets helped or he just grew out of whatever the problems was. I can't be sure, but I do know that nothing else we tried worked. After a few years, I discontinued the tablets because I was worried about oversupplementing him. He eats a high quality commercial dog food.
Secondly, try a paste of termeric and neem leaves. There is a website where you can get all kinds of neem products including the actual leaves (I'm not sure if I'm supposed to mention the site here). I've read that the leaves tend to work better than the oils or powders. I used to volunteer at an animal shelter and we had so many skin problems, and the drugs didn't really help much. Then there is the health issue regarding taking so many drugs. I tried this on a number of the puppies and dogs, most with mange, and had good results. I ground one part termeric with three parts neem leaves, mixed with water, and rubbed it on the dogs once a day for one week (the hairless and irritated areas). You will probably have to confine the dog for a while until the paste drys because the termeric will stain. It won't hurt them to lick if off either because the neem is good internally as well. I don't know if it will work for other skin problems, but we had good results on the mange dogs.
Good luck. If you try either of these ideas and they work, I'd appreciate hearing about it.