The common causes of three-month-old babies crying all the time are improper feeding, lack of vitamin D and organic diseases. 1. Improper feeding: As the baby grows older, the stomach capacity is gradually increasing. If parents still feed their babies according to the previous amount, it will lead to the baby’s hunger, which in turn will cause the baby to cry more than. 2. lack of vitamin D: when the baby lacks vitamin D, it is easy to lead to disorders of calcium and phosphorus metabolism, resulting in increased nerve excitability, which will always show inexplicable crying. Some children also appear easy to sweat, irritable and other symptoms. 3. Organic diseases: the existence of organic lesions in the baby can lead to physical pain and other uncomfortable symptoms, which in turn cause always crying, and crying more than the performance. The three-month-old baby is always crying, there may be other reasons, it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.