BPs are not like a cat or dog. They don't go to the bathroom every time they eat. Babies tend to go even less than adults because they are trying to get everything they can out of their food. If you are really concerned about constipation you can soak them in lukewarm water. This usually helps them if they are constipated, but I doubt yours is. They commonly poop when they shed, so l really wouldn't worry until then unless it looks constipated (the tail near the vent may be really swollen).