My name is ***** ***** I have been a Vet tech for 30+ years with special interest in Reptiles and Reptile Rescue.
You are indeed correct the UVB being too weak and a coil bulb can definitely affect the Dragon's mobility, activity level and overall health. Along with the UVB the Dragon should be getting Calcium 5 days a week and a vitamin 2 days a week. The UVB and calcium work together to prevent Metabolic Bone Disease. Which affects the skeleton as well the organs.
Since he is on antibiotics, you need to add a Probiotic like Benebac to aid with the gut flora that is killed off by the antibiotic. I also suggest to bathe the Dragon is a 50/50 pedialyte and warm water. This helps dehydration caused by the antibiotics. You need to also be feeding 20% fres veggies to include collar greens, mustard greens, dandelion greens, butternut squash, escarole, and curly endives. The prey can include silk worms, crickets, dubia roaches and Phoenix worms. They can give variety in prey items and well accepted by most dragons.
I am hoping these few tweaks will help the Dragon.
One last note is the Baskin area needs to be 105*F-110*F, the warm side in the 90's and the cool side in the 80's. The temps can influence the activity level, and ability to digest food.
Please let me know if you have further concerns or need clarification. If I have addressed your concerns, please take a moent to rate my service 5 stars.