I'm sorry the tests didn't give you any answers.

One of mine has allergies. We've never been able to determine what it's to and my vet can't do any testing. Sleet's skin turns black in spots and she get extremely itchy. So she scratches and makes big sores mostly on her belly and front paws. When the itching gets really bad, my vet gives her a shot of Depro-Medrol. It's a steriod, basically a milder version of prednisone. It doesn't address the allgery, but it does knock out the symptoms for several months. Prednisone did nasty things to Sleet's personality. She stays her usual sweet self on this drug and gets to be comfortable as well. Might be something to ask about anyway? (oh, and it's relatively cheap--Sleet gets a couple shots a year at abotu 30 bucks a pop.)