My DS went 13 days between poops when he was 5-6 weeks old. That was the first time he had ever skipped a day pooping. I of course freaked out and we ended up taking him to see our pedi after about 7 days because it just seems *wrong* to go so long without poop! But she said he was fine and sent us home. Sure enough, he pooped a totally normal (i.e., not constipated) BF baby poop on the 13th day. (The poop was huge though!) After that, he never had a 13 day span again, but he did regularly go 3-5 days without pooping until he was about 4 months old. During that time, we could always tell when a poop was imminent because his farts would get stinky. Nowadays I look back fondly on the times when we didn't have to deal with poopy diapers for days in a row! 
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I would not necessarily recommend doing anything to "help" him go unless he seems uncomfortable. There's really no need. For us, nothing we tried worked until he was ready to go - we bicycled his legs and even did a rectal temperature, but nothing happened. After that, we just let nature take it's course.
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During the times when he didn't poop for days, I just kept reminding myself that he was getting so much goodness out of his breastmilk that there was simply no waste left over. He was using it all to grow! I'm sure your little guy is too!