In the picture his beard looks fairly normal. They can turn a lot blacker than that when something's wrong.
There's a wide variation between individual bearded dragons in terms of how often it's normal for them to poop, but younger ones usually tend to poop more often than older ones. Three days usually isn't a reason to worry too much. Do you know how old he is?
If he is a little constipated, a warm
bath might help if he'll tolerate it, but some will tell you that could cause him more stress. Feeding him a little unsweetened/unseasoned pumpkin puree or applesauce and/or olive oil (if he'll eat it) may also help.
Other questions would be what is he eating, and what kind of lights do you have for heat and UVB, and what are the temperatures at the basking site and in the rest of the enclosure. Also, if you have the lights on top of the screen, be aware that you can lose up to 50% of the UVB through the screen.
Not sure what you mean by "gulping", but they sometimes momentarily stick their tongue out. If that's what you're describing, it's normal behavior, similar to a tongue flick by a snake. They're just "tasting" (or smelling) the air. He may be just exploring his new surroundings.
