My 3 week old wont sleep?

im a 1st time mom and the first week was fine but once we were in the second week, my son started not sleeping during the day unless he's in someones arms! i will rock him to sleep and then lay him in his bassinet (with a full stomach, clean diaper, and swaddled) but 10 mins later, he cries and cries until i pick him up. what can i do???