It is not normal for a three-month-old baby to have a bowel movement once every four days, and this is generally considered to be caused by constipation in babies. A three-month-old baby should have at least one bowel movement per day under normal circumstances. If the baby’s bowel movements are less frequent than usual, or if the interval between bowel movements is three days or even longer, then the baby’s likelihood of constipation is relatively high. First of all, if the baby is breastfed, if the amount of breast milk is small, the baby intake is too small and caused by the decrease in the number of bowel movements, you can be guided by a professional physician to add the appropriate amount of formula milk, which is conducive to the growth and development of the baby, and to relieve constipation. In addition, if the baby’s constipation is still not improved, you can give the baby to take bacillus subtilis bacillus granules and other probiotics to regulate the balance of the baby’s intestinal flora and promote the absorption of nutrients in the body, so that the baby’s constipation can be relieved. If your baby’s constipation is not relieved or accompanied by other symptoms, it is recommended to go to the hospital in time for early and regular treatment. The use of drugs should be under the guidance of a doctor.