I think it can be a sign for teething along with the ear fiddling. My little one is the same. Unless they appear unwell and have a temp I don’t think it’s anything to worry about x
My little one does the same thing but most of the time it seems like he’s dancing, funny enough though his tooth had just cut through his gum too and he’s always messing with his ears
Can be teething or just learning a new sensation. My girl does it now when she’s tired too then yawns,
My girl recently learned to say no so moves her head side to side, could that be the case? Or maybe just practicing something knew that learnt as others said
Sometimes they just have worked out they can do it. When mine first learn to do it he would do it all the time. He would also sit up against things and rub the back of his head against it as it was a new sensation
My little one shakes his head side to side when feeling tired, I’m not super worried about it for now.