I think my Mandy was born with an ear infection in her right ear! After the last one my vet told me to clean her ear with 1/2 white vinegar and 1/2 rubbing alcohol soaked and then squeezed out of a baby wipe. (she did say NOT to do this while an infection was present) Mandy has been doing well since I started doing that. She had bacterial infections. Lacey recently had a yeast inflammation in both of her ears. After we treated it I have been cleaning her ears with the same solution. So far so good. As far as food related my vet said no on both and Lacey never had the yeast problem until she was four and has been on the same food since she was a puppy.
Good luck with your pup as ear infections can be terrible, I know!