Soothing a baby: finger sucking and more
Sucking is a healthy, self-comforting behaviour for newborns. A three-week-old baby will resort to sucking their own fingers – or yours – as a way of calming themselves when they are upset or trying to settle down.
Baby carriers and swings to the rescue!
One thing babies this age have in common all over the world is the tendency to build up to an afternoon or evening crying session. This crying doesn't mean that your baby is missing something, or that you're doing anything wrong; it's caused by her maturing nervous system. Of course, knowing that may not help when you're listening to your baby wail. Try to stay calm. Rock, swaddle and sing to your baby. Carry them in a baby carrier during the day – it can reduce the duration of the crying later on – and try putting them in a swing; the motion can often help quiet a distressed baby but if the baby falls asleep they should be put in their own bed on their back.
FYI:
At this age, babies are demanding, so it can be a particularly hard time for you. Lack of sleep and big changes in the old routine can hit parents very hard. Hang in there! Try to think of this as a brief extension of your pregnancy. Rest when your baby sleeps, and be sure to eat regularly.