There are more reasons why a 20-day-old baby cries all the time, which may be due to hot weather, mosquito bites and other factors. There may also be intestinal cramps, vitamin D deficiency and other diseases. 1. Physiological factors: 20 days of the baby is always crying may be too hot weather, too much clothing leads to poor heat dissipation, causing the baby to cry. Baby crying may also be around more mosquitoes, bites caused by itching discomfort, can also lead to the phenomenon of crying. 2. intestinal cramps: 20 days of the baby is always crying may also be the parents of improper feeding, local cold and other factors, resulting in slow intestinal peristalsis, intestinal accumulation of gas, abdominal pain. The above situation will also lead to the baby crying, some serious children will also appear facial flushing, vomiting and other symptoms. 3. Vitamin D deficiency: when the baby’s body lacks sufficient amount of vitamin D, it will also cause irritability, easy to cry, excessive sweating and occipital hair loss and other phenomena. If the baby does not get timely treatment, it will also appear square skull, O-shaped legs or X-shaped legs. There may be other reasons why your 20-day-old baby cries all the time. It is recommended that you go to the hospital in time for a complete examination to determine the cause of the illness and then give targeted treatment or therapy under the guidance of your doctor.