[theBCnut]

First, has your vet done bloodwork on your dog lately? There are a few things this can be, but the first that comes to mind is thyroid disease. Second, gather ingredient lists from the foods you have tried and try to figure out what they may have in common. Did they all have chicken in them? Grains? This may still be a food allergy, but it could also be environmental. It could also be a systemic infection.