Your baby may have colic if he or she cries excessively over several days. Although this crying can occur at any time, it usually gets worse in the late afternoon and evening. Colic usually appears in the first few weeks after birth and the cause isn't known. It generally lasts for three to four months.Research shows that babies with colic continue to eat and gain weight normally, despite the crying. If your baby doesn't, you should see your health visitor or GP.