Babies should poo daily, once or twice or more. They also can dehyrdate easier than adults.
They don't always recognize standing water (water dish) as
drinking water. You could try
bathing the dragon daily to help. Luke warm water(or a bit warmer, but not hot), up to the arm pits, for 15-20 minutes daily. You may want to hold the baby with the vent (area where they poo) in the water and head above water the first few times to be sure he doesn't drown. You may have to change the water during
bath to be sure it is still warm. This helps
hydrate them and will help with poo also.
Another thing is to be sure the basking temperature is good. The basking temp should be around 105-110f (40-43c). You will need a good way to measure temps.