Thanks for the replies - I guess the thing that I am most worried about is the lack of interaction and therefore lack of learning because he is asleep so much.
I think he's probably a little behind in milestones (I told myself that milestones don't matter and not to take notice - but I couldn't help it, I took a peek at what he's supposed to be up to!).
He has started chatting but only to selected people and you have to work on him to get him going (he's not a baby that gives out smiles willy nilly!).
Might just be him. Time will tell I guess!