I have been told, that it's VERY common for breastfed babies to go without pooping for around 10 days. I freaked out the first time DS did this, but was all ok in the end. He was also a poo a day baby. LOL
It is probably the fact that now that your bub is a little more active, everything that he eats, he requires for energy. I have always though of poo to be an excess of energy that your body doesn't really require ( especially in babies) but correct me if I am wrong.
If he is still having plenty of wet nappies and is pretty normal and happy, he should be fine.
I would give it another 5-6 days, and then call you MCHN.
If you are still worried, give you MCHN a call