My baby is just over 3 weeks old. i am doing a combo of formula and breast milk and she seems to be constipated. has not had a dirty nappy in 3 days?

Constipated ?: Constipated means dry/bulky stools at that age. If it is soft when he does go it is normal. Breast fed kids can go a little every feed or once a week. Adding formula usually makes them go daily, but a mix may be less often. Infants ack strong bell muscles so they must tense their breathing muscle to poop & often appear to struggle.