My son also had constipation&would go only every 5-7 days&cried then. I was told he may have Hiersprung's Disease, a serious & sometimes fatal condition, in which part of the colon muscles have no nerve endings to push the stool along. However, he was gaining weight&didn't have any other symptoms. I read food allergies can cause constipation. I mention this to the gastro doctor & he agreed. Gastro Dr. did a RAST test which is more accurate than skin test. My son was allergic to wheat, rice, egg, milk & avocado. He has been off these foods for 1 month now and is having 1-3 stools a day!!!Hooray! We found our answer. See a Ped. Gastro Dr., Definitely try a RAST test and eliminate the foods. Also have him drink lots of water and eat fruit&veggies. Good Luck.