Have you changed anything in his diet? New foods? More table food instead of pureed? Giving him more food than usual before bed? Did you change his bedtime and now you are putting him to bed closer to the last feeding? Is he teething? If he is, is more than one tooth coming in? I would just try to answer these questions and any other questions you can come up with. Come up with more questions by thinking about what's all been going on the past week with him. And that might help you figure out what's so different about this past week. When my son was that age and got more than one tooth at a time he'd poop up a storm. He'd be pooping all day. (Not literally, but you get what I'm saying, hehe) Good Luck!