My Titan, who's a year old & 550g, has YF and it's horrible, It has spread all along his back, over his head, around his eyes, and under his arms and on his belly. The only way to determine if it is YF is a biopsy, which can be expensive. There are other funguses they can get, so you can also cover the spots with an anti-fungus cream. So this is what I do for Titan, as I have 5 other beardies. He's in my bedroom so he's quarantined away from the others. I use disposable gloves to handle him, as I don't want to touch him, then the others & possibly spread it. I did have a biopsy done and that's how we figured it out. Caught it in 2 weeks as the first month my vet thought it was bacterial & he had shots & creams, but it spread. He's on an anti-fungal med called Itraconazole and the cream is called clotrimazole 1%. I also "paint" him with Betadine & water 1:1 before I put the cream on. I give the med every day but put the Betadine & cream on every 2 days. To help his immune system, I'm giving him echanacea (with no alcohol) liquid 3 drops, 1 tsp bee pollen granules that I melt in hot water, then add a bit of cool water and feed by syringe, serrepeptase for pain & inflammation (as he flinches when he's touched, so I know it hurts) and acidophilus for his tummy to make sure he keeps eating. If he doesn't eat his greens I give him Carnivore Care mixed in with butternut squash babyfood. He gets his regular calcium & vit/min, too. It's worth all the work to cure this dreadful disease.
I've talked to a few people on the Facebook rescue forums I belong to, and I keep being told it's not cureable and can be fatal. So I'm ignoring that as I just want him better & don't want to thin that he'll have this forever.
If there's anyone else on this site who's fought Yellow Fungus and won, please let us all know.
I'm so hoping it's not Yellow Fungus for your little one, but a vet visit is mandatory to figure it out.
Good luck & take care
Deb