Throughout the last month a 2-month-old baby had paroxysms of irritability, restlessness, and crying that start for no apparent reason. Such episodes occur during the feeding or immediately after. Noticeable relief often occurs after defecation. The duration of the episodes is approximately three hours a day. Between the episodes, the child is calm, has a good appetite, the increase in body weight is physiological. What is the most likely diagnosis in this case?