Poor little man has been pawing at his mouth, intermittently, whilst sticking his tongue out as far as he can. Even yelping in pain on one occasion. 
Took him to vet's today. She had a look in his mouth and said it's his adult teeth coming through.
I've never experienced a teething kitten having such a painful time with it. this doesn't affect him all the time, only happening a few times over several days. This aside, he's his usual happy self, still enjoying his food.
Do any of you have experience of this?