Baby shaking head

Does anyone know why my LO would be shaking his head side to side like he is saying “no”? I wondered if it was a way of showing he was tired. Last night we had the worst night of falling asleep-he’s never cried so much so I wonder if it’s a teething thing or an ear infection thing instead? He also doesn’t just do it while laying down, while he’s sitting in his high chair or on his tummy too.