Yeah, they didn't test for Yellow Fungus if they didn't send it out to another lab, and I'm sorry to say that he most definitely has Yellow Fungus, and unfortunately it's very advanced now because that vet doesn't have a clue what he's doing, no reptile specialist would see even beginning Yellow Fungus and not do a Skin Scraping test and send it out...Is he an "Exotics Vet"? He may be the only vet in your area that will see reptiles, but he's not a reptile vet...I'm so sorry.
Yellow fungus grows internally as well as externally and that's why it's usually lethal, especially to young beardies. The oral Antifungal medication Voricozanole is 100% necessary, plus an additional prescription antifungal cream and injections. You also must use either F10 disinfectant or bleach and hot water to disinfect EVERYTHING in his tank, inside and out, his lights and fixtures, everything at least once a week, and remove anything from his tank that isn't necessary, no plants or extra rocks or hammocks. Just his basking spot platform. And only use paper towels in the bottom and change them out whenever they get dirty and then once a day on top of that. Wash your hands every time before and after you touch him or anything in his tank, he can't get an additional bacterial infection, and you can keep spreading the Yellow Fungus to other parts of his body if you touch him and don't wash your hands in antibacterial soap. It's an awful disease...
No more baths at all for him, it will only spread Yellow Fungus, he must be completely dry all the time. He needs to get to an experienced reptile specialist vet or a certified reptile vet immediately, before the disease starts to cause the need for amputations. I'm sorry, this isn't going to be easy, and young dragons typically don't live, I'm not trying to upset you but rather prepare you. I've seen them lose limbs at the stage he's at, and you may want to think about what's best for him, it's quite a painful disease at this point for them. Either way he needs a Skin Scraping test to absolutely confirm it ASAP, but that's pretty clear as to what it is. Then you need to decide whether or not to try to put him on the Voricozanole and external prescription meds, but keep in mind that most dragons are on the meds for 6 months to a year, with month long breaks in between because the meds are so harsh, so please think long and hard about what you want to do. Had it been caught earlier by that "vet" I'd not hesitate to treat him, but unfortunately it's pretty advanced...