It could be many things. A skin yeast infection? An allergy (contact or food?).
If it's not going away you need to get to the vet, specially if it's bothering your dog.
MACH3 Bretta Lee Wildhaus MXG MJG MXF MFB TQX HIT CGC TC
Glory B Wildhaus AX, AXJ, XF
"How is it one careless match can start a forest fire, but it takes a whole box to start a campfire?." ANONYMOUS