Sometimes just plucking the ears can cause an ear infection. Any time you are pulling hair out you are opeinig a hair follicle for possible infection. I had a dog once that would get an ear infection if you did not pluck his ears because of all the hair, but he would always get one AFTER plucking. No win situation. Also some dogs have reactions to some ear cleaners. Look in that ear and see if it looks red or inflamed or has a smell. If so, get it to the vet pronto.