A 40-day-old baby crying and not sleeping at night may be caused by dietary factors, gastrointestinal factors or vitamin D deficiency. Treatments include dietary adjustments, general treatment and so on. 1. If it is caused by dietary factors, such as insufficient feeding, insufficient breast milk, etc., these conditions can lead to frequent hunger in the baby, due to hunger can lead to crying and not sleeping. Timely feeding of the baby can relieve the crying and fussing of the baby. 2. If it is caused by gastrointestinal factors, such as too much breast milk before going to sleep or the abdomen is cold, resulting in food accumulation, indigestion, gastrointestinal dysfunction, causing abdominal distension, abdominal pain, intestinal colic, gastrointestinal spasms and so on, can also cause crying at night, do not sleep. You can massage your baby’s abdomen to improve gastrointestinal function, reduce the amount of milk in each feeding and increase the number of feedings to adjust. 3. half a month after the birth of the baby should routinely supplement vitamin D, especially in the northern region of the child’s exposure to sunlight time is relatively small vitamin D demand is relatively large, the lack of vitamin D will lead to the baby crying at night, timely supplementation of vitamin D to the baby can improve the situation. You need to actively observe the baby’s situation, if there is an abnormality, you also need to take the baby to a professional hospital for examination, in the doctor’s help to reasonably carry out the treatment and conditioning.