could be winter as skin gets dryer in winter
so your dog is 5? has this been ongoing issue or recent? If recent due to age I would have thyroid panel done next blood draw to rule out hypothyroid as allergies show up from age 6 mos to 3 years old
here is a thread with info i wrote on it as been dealing with this since dd was 6 mos old it may help
http://www.yorkietalk.com/forums/yor...y-what-do.html