That's quite a bit of weight loss. It sounds like you've already posted about this on here? Have you answered the usual enclosure/set-up/diet questions already? If there is a history of posts here I'm not familiar, and I don't know the history of his illness...If you have already posted about this, can you link that post or posts?
One thing that I can say, regardless of the illness history, is that if your beardie has not had an appetite for a long period of time to the point that he's losing enough weight to make a difference in appearance, you certainly should not be waiting "A FEW WEEKS" to take him to a Certified Reptile/Herp Veterinarian who has experience with Beardies and can run proper tests to accurately diagnose what's wrong and and provide the appropriate treatment! A few weeks? I'm sorry, not trying to be harsh or rude, but if you're really that concerned (and you should be) then you need to rearrange your schedule, take a sick day or a personal day or just call in sick on the day of his appointment (or even just take a few hours off to take him if you have a Certified Reptile vet close). He cannot wait "a few weeks" if he's not eating, hasn't eaten in a very long time, and is losing quite a bit of weight. If it is allowed to continue "a few weeks" and does continue the same way it already has happened, imagine how much weight he will have lost "in a few weeks"...
Up to you, but sometimes home remedies and natural treatments are not good enough. Again, I don't know what you've already tried or what the history of this issue is, but I do know that waiting "a few weeks" to even get an actual diagnosis and start appropriate treatment is a huge gamble and it may be too late at that point. And the reason I'm pushing this isn't because I'm trying to be dramatic, it's because I'm tired of seeing this exact situation over and over and over and over on here, every single day, and the poor Beardies suffer, are in pain, are put through so many different things their owners are hoping will work, then the beardie either dies without ever seeing a vet, sees a general vet that has no idea what they're doing and then dies, sees a reptile vet, is diagnosed and starts treatment but dies anyway because they waited too long to take them, or they just disappear and never update on here again, most likely because their beardie died...It's frustrating and depressing, and sometimes absolutely infuriating. I'm not directing that at you in particular, I just don't want to see your beardie end up the same way...