Synchronicity, might be worth keeping in mind that Sam, on the same formula as you are using would poo every 4 days like clockwork. He wasn't constipated, and we spent a lot of time giving him coloxyl trying to get him to poo... but he didn't need to until he hit that 4th day, and you could almost set your watch by it! Changed when we introduced solids, but he was like that for a very long time.

BW