Dog licks throughout the night

But not during the day. This is seriously disturbing my sleep because he has a loud lick and he wakes me up with his licking at least three or four times a night, if not more. Then come the daytime he's so tired having spent the whole night licking that he sleeps like a rock.

He's not licking anything in particular, he's lick his foot a bit then his leg a bit then the bed a bit... I've checked and there aren't any wounds or growths or anything for him to be licking.

How do I stop this?