I too have a dog (lab) with floppy ears (mixed with RB Coon), vet bills, cultures etc. Finally figured out he's allergic to everything.
Grain, beef, chicken, fillers...changed his food to Taste of the Wild, Pacific Salmon and his ears cleared up.
Note, they were so bad and bothered him so much, while shaking his head he developed a large hematoma. They aren't something you want to wait on.
Good luck, hope your pup feels better soon (and you can get some relief)