Why is my almost 3 week old baby doing this?

At only 3 weeks their schedules will change constantly. He might have a touch of colic. But sleeping that long at night is GREAT. Have you tried swaddling him tight? He wants to be held because he just came out of a very tight womb and he is still not used to this crazy world yet. He won't sleep during the day because he sleeps so long at night. He just wants to be close to you and there is no problem with that.