How will I know if my child has colic?

Crying unconsolably. A common definition of colic is an infant who cries for more than 3 hours a day, 3 days of the week, for more than 3 weeks. Although no one knows for sure what causes it, colic is fairly common, starting a few weeks after birth. Luckily, this condition goes away by about the third month of life. The main thing is to make sure your baby's crying is not caused by a serious condition.
Pattern of crying. Colic is excessive crying in young babies. The most common pattern peaks at about 6-7 weeks of life, and most of the crying occurs in the evening during very specific hours-- you can almost set your watch by it.
Crying excessively. Pediatricians define colic as crying for more than 3 hours a day, 3 days per week, usually for 3 weeks or longer. There is usually no discernible reason for the crying. Most infants stop being colicky by three months.