You are in Az so you may be dealing with a foxtail along with an
infection. Your best bet is to have your vet look down in the ear canal
with an otoscope to assure there's not anything causing the irritation.
At that tie they can do an ear swab to establish if it just yeast or
possibly something else and that will determine the type of medication.
Good Luck!
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Let me know if you have any other questions
Good Luck &
Best Fishes