Seems more satisfied with bottle?

I mostly nurse my 3 1/2 week old & sometimes give him 1-2 bottles of milk I pump during the day. He seems more satisfied when he gets a 3 oz bottle & will go 2-3 hours between eating than he does when he nurses. He never seems full when he nurses & will want more 1 hour or even less later. Can he not be getting the full 3 oz from me when he nurses? Thinking I might need to exclusively pump.