My 3.5 week old sleeps all the time. He has a few awake periods but they're very brief. He must sleep 20 hours out of 24 I reckon, or that's how it seems. He's gaining weight and feeding well but my first child never slept very much at all so this is a bit alien to me. I keep worrying something must be up with him? Or do I just enjoy it while it lasts? TIA