Babies can poop anywhere from 8 to 10 times a day to once every 7 to 10 days and will still be considered just fine as long as they are not uncomfortable.
Baby can get constipated when you switch to a new food, like from breastmilk to formula, or when you introduce new solids. If baby is constipated, the poop will come out as hard balls or she will be passing a lot of gas. Beware of black, red or maroon poop which could mean there is blood in it. Blood can be a sign of something more serious.
Baby at 3 weeks old is still young and should not be introduced food that can improve constipation. You can cycle baby legs and massage her tummy to help get her bowels moving. You can change her formula or your diet to help. Add in some fruits and veggies such as pears and broccoli.
If all the tricks do not help, it will be better to talk to your doctor for advice.
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