I would first try to increase your milk supply so that your son is getting just breast milk, as it is so much easier for babies to digest and move through their systems & is so much better for them all around. You can try pumping, but the best way to increase your supply is nurse, nurse, nurse!!! The more you nurse, the more you make, and even if your breasts feel empty, they are always producing milk - ALWAYS. Most people don't know that and end up giving up bf'ing. Look on La Leche League's website (www.llli.org) for more info, and call on of the leaders for more help w/ nursing/increasing supply, as well as other ideas to help your baby w/ constipation (they have helped me w/ so many topics, and I don't know what I would have done w/out them). Good luck, and keep nursing!!!!