A 15-day-old newborn crying all the time may be caused by physiological factors, calcium deficiency, eczema and other factors. 1. Physiological factors: frequent starvation, high or low temperature, infrequent diaper changes and other factors may cause newborns to cry a lot and return to normal after eliminating the above triggers. 2. Calcium deficiency: when the newborn lacks calcium, it will also cause the newborn to cry more than usual, and may also be accompanied by pillow baldness, restless sleep and other abnormal manifestations, which may affect the physical development in serious cases. 3. Eczema: may be related to environmental factors, may induce baby eczema, cause tingling, itching and other symptoms, will lead to frequent crying of newborns. A 15-day-old newborn crying all the time may also be related to other triggers, accompanied by obvious abnormal manifestations, parents are advised to bring their children to the doctor for timely examination and treatment.