I know you posted this two years ago. Hope your dog has gotten better by now. My dog (JRT x Chihuahua mix, 11 mo old) is just having a very similar symptom. I'm so worried. I took him to a vet earlier today and they are doing some checkups at this moment, including some x-ray and maybe blood work. My dog does not seem to have any ear infection so far.
I wonder how your dog is doing since then. Did you find anything after all? If you could respond to this post, it would be highly appreciated.