Well... You need to be replacing your UVB in Dec, so this could play into the energy level.
It's also winter and as it sounds like you are in the UK, I know it's getting chilly.
Beardies don't go into a full brumation cycle until they are adults (if at all), but I do feel that mine were affected by cooler temps even as juveniles.
I'm not sure if it will help, but you're gonna want to bump your basking temp just a bit. Try to get it btwn 100-105.
You're also going to want to add some more bitter greens.
In American English good staple greens are : collard, mustard greens, endive, escarole or dandelion greens...
for the Brit translation PM Dantro, AuntyLolo or Mark Thorpe- I can never remember the different names across the pond.
Also at 10 months, he should be slowing his bug eating and going more after the greens. Is that happening at all? Around that age you can switch him down to one daily bug feeding and limit him to around 30 feeders a day depending on his appetite/weight.