Crying of 4-month-old babies may be related to hunger, indigestion and vitamin D deficiency. 1. Hunger: Breast milk may not be enough for your baby as he or she gains age and weight after birth. This is the time to increase formula feeding as appropriate, depending on the circumstances. If the amount of feeding is not enough, the baby will often be hungry and will cry a lot. 2. Indigestion: It may be that eating too much or eating with more air into the intestines, causing gastrointestinal discomfort, bloating and other symptoms, the baby showed crying phenomenon. 3. Vitamin D deficiency: the baby out of the activities less or food vitamin D deficiency and other causes, can lead to the baby vitamin D deficiency, crying and so on. 4 months baby crying may also have other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.