B.
You can give him prune juice in a bottle mixed with milk or formula. If that doesn't work, you can also buy Benefiber and mix that in with his breastmilk or formula in a bottle. My daughter is crazy constipated and my pediatrician said that Benefiber is very safe for babies and children. Start by giving him 1/2 tsp once a day. If that doesn't get things moving, up it to a 1/2 tsp twice a day and go up from there. Just increase slowly so you don't end up over-doing it. Good luck - juices and all the other normal tricks weren't enough for my baby and she was miserable. She now gets Benefiber twice a day and it really helps.
B.