What causes extreme itching in dogs? I have 2 young dogs that have begun scratching and biting thems

They get bathed once a week or so with flea & tick shampoo. Recently I switched to a shampoo designed specifically for allergies and it hasn't made any difference either. They are both white dogs and no fleas are visible anywhere on them. They both exhibit symptoms of ear mites and are being treated for that. They are scratching and biting their hair off in spots. I can't afford a high vet bill and am at a loss as to what to do for them. They seem miserable. Please help!

It sounds like skin allergies, likely caused by food. Check your dog food, to see if there is corn in it (most common allergy)

Many, if not most, white dogs don't tolerate corn.

Feed a high quality food with no corn, soy, food colorings, or wheat.

This supplement would also be of great help for any skin problem> http://springtimeinc.com/product/88/2

You may be bathing them too often. Over-bathing can cause dry skin that will lead to itching. Cut back to once a month and just brush them between baths. Regular grooming will stimulate oil production in their skin to keep it from drying out and will keep the coat healthy, too.