My cocker spaniel had exactly the same symptoms recently - no visible signs of an ear infection (and has never had any issues with his ears before - quite unusual for a cocker lol), the vet took a look down there and noticed there was a little redness and wax, but not a full on infection. She wondered why he was making such a fuss about such a small thing! He had Surolan ear drops 2x a day for 2 weeks and that cleared whatever it was up.
Our 10yr old dog yelped twice in pain today when her ear was accidentally brushed by my hand. We took a look and couldn't see anything obvious, she was happy with us looking and stroking her head. I wondered if it was the beginning of an ear infection and wanted to know if anyone else had experience with this.
We are taking her to the vet tomorrow morning first thing. She has been a bit subdued but still eating and drinking OK.