Do you live in the country in MN?
My 4-year-old hound mix, Priss, has problems in the summer months starting about August. She will lick her feet until they are red and the fur is almost gone. I have tried all kinds of medications, shots, and changed her diet, but it is something environmental. I've even taken her to different vets to see if someone might have a solution.
Most of the medications are steriods; they work for a week or so, then are ineffective. I won't use them anymore. Priss bloats up like a balloon!
My vet thinks it is either a particular weed that grows this time of year or possibly a mite or small insect that is invisible to the naked eye. I wash her feet in vinegar and water when she comes in the house and have started using Willard Water, http://www.dr-willardswater.com, too. Sometimes, I use a diluted solution of tree tea oil to soothe the itching.
Priss smells like a dirty sock from licking her feet when she is troubled by allergies. Also, she runs a low-grade fever, especially in the morning. I give her 1/2 a baby aspirin and wash her face with cool water.