Okay he definitely needs a dependable reptile/exotics vet soon. For a young dragon to suddenly go down hill, there would usually be one of two problems, parasites, or the beginning stages of MBD. If he has parasites, your vet will do a fecal and basically de-worm him, end of problem. Fairly cheap.
Metabolic bone disease
(mbd) is another matter. It can become deadly quickly and it happens because the animal doesn't have enough calcium. This is especially dangerous in young fast growing animals like baby beardies because they are growing bones that require calcium so quickly!
Yes, you should have had a UVB bulb immediately, they can't live without out, not having it keeps them from being able to process vit. D3 and calcium. Also, the bulb you have now is cheap and likely does not have the microwatts necessary to do the job. You need a reptisun 5.0 or 10.0 depending on size of the tank. These are available at large chain pet stores
such as petsmart, petco, etc.
Also you should have a vitamin supplement to dust your crickets with that includes calcium and vitamin d3.
If it's metabolic bone disease your vet will likely give you a strong calcium supplement to give for a few weeks, and may also give an injection.
In the meantime, whether it's parasites or mbd, not eating or drinking is dangerous for a little guy, so make an appt immediately but you may also want to force feed. This gets kinda gross, but on the plus side can help you build a trusting relationship with the new guy. You need to get something with electrolytes and not a lot of sugar (pedialyte, gatorade), a jar of baby food fruit, a jar of high protein baby food such as beef or veil, etc, and some reptile vitamin supplement dust with calcium and d3 (again available in most chain stores.) Mix all of this together and put it in an eyedropper or needleless syringe. Administer as much as you can manage about twice a day until you can see the vet. This will at least keep him from dehydrating and going down hill further.