My beardie sometimes goes a week and sometimes even close to two weeks without going. I started to get worried so I took him into the vets and had him checked for signs of impaction, and I even got bloodwork done on him. They told me that he is a perfectly healthy reptile, he just doesn't go all that often. I have a feeling that since he was in a small cage at the reptile place I got him from (i think it was a 20 long shared with another beardie...he was about 12" long and the other was about 15-16"...the reptile place has since done some housecleaning so to speak, and now they keep beardies in larger enclosures), maybe he's just never wanted to go because he had to live in confined quarters with it before. I mean, with how many reptiles the place had to take care of, they were lucky if they were able to clean every cage every day (like I said though, they've since changed and hired help). I just started thinking about the psychological aspects of it because I adopted a neglected uro that will hold in her poo until I take her out of the cage. I'm trying to get her used to the fact that she's not still in the disgusting 10 gallon tank she was in before, and that I will clean it up when she goes. I also heard from a local petshop that a guy got a baby bearded that absolutely will not go in it's cage either. They tried keeping it in the cage for about a week and then as soon as they took it out it went.
My beardie doesn't usually go outside of his tank though, it just takes him a while. I think he may just have a wierd metabolism, or maybe the fact that he isn't eating his veggies is attributing to it. But that will soon be changed. This summer I'm weaning him onto a mainly veggie diet.
That's my take on it. I would still have him checked out by a good reptile vet if the problem persists.