What can a do for my month old, he's constipated?

See pediatrician. Take your baby to the doctor. We do not give over the counter medicines to children that young, and you and the baby's doctor need to work together to determine the cause and the possible ways to help. If the baby is really constipated then a change in formula may be needed. If the baby is breast fed, that is different. See doctor to make sure it's not something more serious also. Good luck.