Hello mom. Babies with colic or infantile colic are healthy, well-fed babies who cry long, often inconsolable for no apparent reasons in the first three months of life. It usually starts a few weeks after birth and often improves by age 3 months. By ages 4 to 5 months, the majority of babies with colic have improved. Some theories or beliefs about the cause of colic include excessive gas in the tummy, milk allergy, bacteria imbalance and so on. However, no one is really sure.