Newborn can’t sleep

3 weeks is when babies naturally start getting less sleepy- I think melatonin levels that they have at birth drop naturally at that time. To avoid an over tired baby, put baby to sleep/nap earlier. Try to follow feed, play, sleep routine. Aim for full feeds before baby gets too sleepy- a sleepy baby can’t eat well, and a baby that isn’t full can’t sleep. You might not get the timing right for the first few times- don’t be discouraged! It’s a constant process of trial and error and adjusting as they grow and change