Colic is a digestive problem that occurs between 3 and 4 weeks, and lasts as long as 3 months of age. It usually strikes after feedings, and can be extremely painful. Another form of colic- Irritable crying, usually occurs at one regular time of day but does not show any signs of pain or gas. It sounds like your son is getting enough to eat. Sometimes the bottle is what is causing the colic.
Some babies have a sensitivity to formula.
You may want to try giving him soy formula, or even try breastfeeding exclusively. In my daughters case, the supplemental bottle was making the colic worse. When my daughter had colic, I discontinued bottle-feeding and that seemed to help her significantly. Breastfed babies nurse not only because they are hungry but to be comforted as well. Your son will continue to nurse, even if he has had enough to eat.