He doesn't defecate often, is this a sign of constipation or diet problems? I'm feeding him fuzzies right now.
It really varies from one individual to another there is not set schedule however I would guess that because you are feeding fuzzies most of the prey item is being absorbed for his growth.

I would recommend to feed a prey slightly smaller than the girth size, keep in mind that most hatchling BP are started on hopper mice and quickly move to small to adult mice.

As far as refusal if your BP refuses just wait another week, offering too soon after a refusal will only cause stress and lead to more refusal.