If he is fine while he is sleeping or eating then it isn't teething because a child that is teething doesn't want to do either of those. It is all about not being down on the floor with the other kids. Try putting him in an exersaucer or similar or even in the highchair in the playroom - ideal if you can lower the chair closer to the floor and give him some toys but no food. He may just need the security to get used to the group.