Yes, you absolutely need a better
UVB light, those Reptisun don't emit nearly enough UVB for a beardie, and you also have them mounted on top of a mesh lid, and that will block up to 50% of what little
UVB light they do emit, pluses your tank is very tall and those T8 bulbs must be inside the tank and within 6-8" of his main basking spot. Plus, the compact bulbs focus the light on one spot, he needs a long tube to go right alongside his bright white basking bulb over top of his basking spot. So he's basically getting no
UVB light and this could very well be why he's not active now, it finally caught up to him.
Based on your tank length you need a 24" Reptisun 10.0 (never a 5.0) long tube
UVB light and matching fixture. And I'd get the T5 High-Output version rather than the T8 version, based on the size of your tank. The 10.0 T5 High-Output version can sit on top of the mesh (it's strong enough) and can be up to 11" away from his basking spot as long as it's right alongside the bright white basking bulb. The T5 High-Output also only needs replaced once a year. The cheaper T8 must be mounted inside the enclosure and within 6-8" of his basking spot, and replaced every 6 months. Go onto Amazon.com and search "Reptisun 10.0 T5 22"...The T5 22" is actually the 24" equivalent...Then choose the cheapest one, and scroll down to the package deal that adds the 22" florescent fixture that's rated for a T5 tube...I'd get it ASAP so you can figure out if this is the issue or not...A Mercury Vapor Bulb like the MegaRay is option #2.