How old is your beardie, and how long have you had him?
If you've only had him for a couple of days up to a week or so, then it's not uncommon for them to have a bit of relocation stress that should pass within a week. As Cooper said, if your dragon is currently shedding, regardless of his age, then this too can slow their appetite, so just give him a few days until the shed is over, you may also want to give him a quick, daily, warm
bath to help with the itching if he's shedding.
If neither of these things are the case, he's not shedding and he's been with you longer than a week or so, then usually when they stop eating and/or become lethargic and lazy, it's because they haven't been getting adequate
UVB light, or their temperature zones within their tank are wrong, or a combination of both. So it's a very good idea to go over some of your basic husbandry information to ensure that the lights you have over her are proper (people buying the wrong UVB lights is the #1 reason that Bearded Dragons become sick), as if you got any information about what lights to buy for him from a pet shop employee, a breeder, or the internet, chances are that you got very bad information.
If you can post some photos of your beardie and his entire set-up, showing how you have his lights set-up over the tank, this is extremely helpful. You can upload photos using the "User Image Uploader" in the Task-Bar at the top of the page, then after you upload all of the photos to your account, then hit "Post A Reply" and in the message box click the "XIMG" button right above the message box, and insert each photo into the box.
Then can you please answer the following questions about your dragon's set-up (The information about your lights is printed directly on the bulbs/lights themselves if you don't still have the boxes):
What size tank/enclosure is your dragon in? (gallons or dimensions)
What substrate do you have in the bottom of his tank? (sand, wood chips, tile, paper towels, carpet, etc.)
EXACTLY what
UVB light do you have, meaning the Brand Name, the Wattage, the Strength (T8 or T5 if it's a long tube), and what type is it, meaning is it a Compact, a Coil/Spiral, or a long tube?
How old is your
UVB light? Do you have it sitting on top of a mesh tank lid? How far away (in inches) is the UVB tube from your dragon's basking spot/platform? How many hours each day do you leave the
UVB light and the Basking Bulb on?
If you have a long UVB tube, does the bottom of the long, tube fixture it's inside have any type of clear, plastic cover on it that is filtering the light coming from the tube?
What type of thermometer are you using to read his tank temperatures (Stick-On, Temperature Gun, or Digital Probe on a Wire)?
What are the current temperature readings for his Cool Side Ambient/Air Temperature, his Hot Side Ambient/Air Temperature, and then his Basking Spot Surface Temperature?
What does his normal, daily diet consist of?
How many times a week do you give him a Calcium Supplement? A Multivitamin Supplement?
