Thanks for answering my questions.
As someone who lives with an allergy dog herself, I can completely understand how frustrating it can be when you're trying to figure out what is causing your dog to be so miserable.
With my pup, I had my vet do VARL testing (more info here: http://www.varlallergy.com/ ), which determined exactly what he was allergic to (turns out he's allergic to ragweed and a specific type of pollen), which made it easier to control his contact with the items he's allergic to. As a side note...many, many, many dogs are highly allergic to corn and corn products, so it could very well be that if any of the dog foods you're using contain corn, that could be part of his problem.
We also began using the medication Atopica (more info here: http://www.atopica.com/ ), which helped control his itching and made him a happier guy. Atopica is sort of the 'big gun', and once we got my dog's allergies under control, we were able to switch to Temaril P instead (which is less expensive and it only takes 1/4 tablet once a day to keep my dog's allergies in check).
In the meantime, there are some over-the-counter, home remedy type things that you could try to keep him more comfortable:
*For some itches, we suggest soaking in a baking soda bath. Adding 1 cup of baking soda to a tub of warm water and then soaking 30-60 minutes. Take dog out and let them air dry (this works best if done outside or in an area where there isn't carpeting as wet dogs drip...a lot). Local itches can be covered with a paste of 3 parts baking soda to 1 part water.
*Oatmeal is an old favorite. Adding 1-2 cups of finely ground oatmeal to a warm bath sometimes can calm even the most irritating of itches. Just make sure the water isn't too hot, or you'll have breakfast for a week in your tub!
*Lots of folk remedies call for using lemon to help with itching. They contain anesthetic and anti-inflammatory properties that may help reduce itching. If nothing else, your dog will smell good!
*Splashing the affected skin with basil tea can help reduce itching as well. Basil contains large amounts of a substance called 'eugenol', which is a topical anesthetic. To make the tea, place 1/2 ounce of dried basil leaves in a 1 pint jar of boiling water. Keep it covered to prevent the escape of eugenol into the air. Allow to cool, then dip a clean cloth into the tea and apply to itchy skin as often as needed.
*Mint tea works about the same way, except the anti-itch property is menthol, not eugenol. To make the mint tea add 1 ounce dried mint leaves to 1 pint of boiling water. Cover and allow to cool. Strain the leaves out and then dip the clean cloth in the tea and apply to the itchy areas.
*If you're saving the basil for spaghetti sauce and the mint & lemons for a glass of lemonade, you can use thyme tea. Once again use 1/2 ounce dried thyme leaves and 1 pint of boiling water. Cover and cool. Strain and use clean cloth to apply to affected areas.
I hope this helps!!