Your dog likely has allergies. These are all classic signs. Talk to your vet about an anallergic diet, an antihistamine and a product called Burow’s Alluminum Acetate 2%/HC 1%. I have one dog that was constantly on medication for yeast in his ears. I put 2 drops of the Burow’s in each ear, twice a week, and keeping my fingers crossed he has not had an ear infection for several years now. He still has skin issues at various times of the year, Spring and Fall but things have been much better with the steps above. There are many other products that can be used but start out conservatively and see what works before you go in all the way.