First welcome to this site and congrats on your new beardie!
There is something that beardies suffer from when they change households, and it's called relocation stress, so that could be it. It just means that your beardie is stressed at his new situation and can put off all his normal routines, plus he's not longer with his original owner.
It would also be good to go over your setup, as it's not always the best, so if you could answer these few questions, I'll see if it's something there or relocation stress, which can last 2 weeks. The previous owner could have been making some mistakes.
What type
UVB light are you using? How close can your beardie get to the
UVB light. Is it a tube and if so is it on top of the mesh tank or inside the tank?
What are the basking temps and what are you using to measure them?
What sized crickets are you offering your new beardie (needs to be smaller than the space between their eyes)
And you dusting the crickts with calcium without phosphorus and with Vit D3? And also with vit/min. An adult beardie would need a meal dusted with calcium 3 times per week and a meal dusted with vit/min once a week.
Did your beardie eat greens and veggies with his previous owner? And what kind?
So if you could answer these questions, I could figure out if that's all good & then we can figure out what do to about the rest.
If it's relocation stress, you need to be patient with him and assure him you're his new owner and will take care of him. Did you get his routine from the previous owner? It's important you stick to is as close as possible. One thing I've been told by alot of new owners is they take a Tshirt they've worm, before washing it, put it in the tank for the beardie to nestle in at night, he smells your scent and will get used to it.
So let me know the above info and we'll see what we can do to make your beardie & you more comfy with each other.
I have 5 male adults, I've been raising dragons for 6 years and learned all I know from the good people on this site. My 5 are very easy to handle, love to cuddle and love their routines.