Hi You might have to rule out cow`s milk protein allergy since you say its related to dairy. Give him plenty of water, fruit juices, vegetable soups, fresh fruits, vegetable like spinach, whole grain food etc. Avoid rice based items, potatoes etc. Try to cut down on his formula milk. Instead of cerelac- give him home made food. Please visit your Pediatrician and get any anal fissures ruled out- as fissure is very painful and it sets up a cycle- due to pain child holds the stools, which in turn worsens the constipation. If he has a fissure, he needs a stool softener and local anesthetic gels for about 3weeks to help in complete healing. Hope my answer helps you. Wish your son good health.