Poor beardie, I'm so sorry he's in this condition. Nothing there is caused by any bulb, your poor dragon has serious , advanced fungal infection. He/she needs a very experienced reptile vet only, otherwise they will not help your dragon at all. Lamisil cream can help a bit but there's a possibility that this may be fatal. The oral meds. for this are either itraconazole or voraconazole , they are antifungals so if a vet prescribes you antibotics they are inexperienced and giving you the wrong type of meds. Best wishes , hope for the best but be prepared for a possible bad outcome. It's nothing that you did, he probably was exposed to this at the store. Can you check back at the store and see how the other beardies are doing ? This starts out small but then spreads to what you see now.