I see these ear infections all the time in my foster dogs. My golden rescue also came home to me with the yeastiest ears I had ever seen and vets just wanted to keep putting her under to flush them. This isn't the best place to start since you want to address the cause FIRST, otherwise, you will be flushing all the time and chasing it - you want to get in front of it. And putting a dog under is not a benign event - it takes a health toll each time so not to be done lightly.
Ear infections - especially the just one ear, recurring thing is allergy. It frustrates me when vets don't test the ear material since it can be either yeast, or bacteria or even both. They are treated very differently and many vets just presume and send customers home with solutions that then never cure (an antibiotic will do nothing on yeast for example).
One foster boy I had was 2 years old and his owners had been buying these solutions and antibiotics for his entire life....all I had to do was test, see it was both yeast and bacteria and realize that to cure the yeast, I had to find the cause first (bacteria can be treated, but yeast must be prevented first). Usually the allergy is diet related so I put him on a homemade elimination diet and immediately found the allergy - chicken - once I rid his diet of the offending food, his ears cleared up and have been completely clean since (over a year).
In the case of my golden, I had her on a raw diet from the start so I started evaluating the diet one ingredient at a time, starting with starches (sugars can exacerbate yeast). It turned out that the starches were her problem, specifically carrots, and just removing these from her diet and her ears cleared and have been squeaky clean for the past 7 years.
What sets up the yeast imbalance in the system is another issue - I believe over-stimulating the immune system is the root cause.
So I encourage you to find the root of the ear problem - the medications are just symptom suppressive and will keep you in a "chasing" mode - you will rather prevent these infections in the first place.