Baby wont sleep unless ....

My son will be 3 weeks old tomorrow & lately he's developed this thing where he only sleeps (for a long duration) when he's being held. Doesn't matter who's holding him, as long as he's being held :( its worse at night because he won't sleep unless he's being held or on my chest, which gets uncomfortable sometimes, because he's getting a little on the heavy side for me to only be 3 weeks :/ he'll sleep for about 10-15 minutes on his own then wake up and cry & whine because he wants to be picked up and it goes on all night. I'll hold him until I'm sure he's sleep, but put him down & he's right back up minutes later crying, wanting to be held (or fed/changed, but he won't go back to sleep unless he's on me.) I'm the only one that has him at night, during the day, I have help. What can I do so he can sleep on his own at night? (I know he won't sleep all night because he gets hungry & wet, but what can I do so he'll be ok with sleeping without being held the whole time?)