Hard to say what it is, but it could be pyoderma, which is a staph intermedius infection/overgrowth in dogs...is treated w/ Simplicef for 30 days. A simple skin smear is all it take to diagnose. Has that been done?
Those hard-looking bumps...does anything come out of them?
I'd read up on allergies here:
http://www.yorkietalk.com/forums/die...tart-here.html