Since he's 3 months old (or there abouts), the change in his eating habits is just his growing up ,he's no longer an itsy-bitsy hatchling, he's become a juvenile and he's figured out that his bugs will be there for him 2 or 3 times per day regular as clockwork . He should he on two live insect meals per day at his age.
He will likely simply wait for bugs to blunder close enough for him to snap up as they roam about in his tank while he's basking, any bug that comes close enough is lizard-tukka.
Also , he may be finding the bugs you are feeding him too small to bother with, what size bugs are you giving him, might be worth upgrading the size bugs by a size or two. (I'm assuming he's getting very tiny bugs).
He may simply be about to shed, some beardies go off their food for a while before they shed, very young beardies shed frequently.
You can hand feed him if you want be sure he's getting the right amount of bugs.
At 3 months old Peppa and Toothless were gobbling down up 20 medium-small (1/3 size) crickets and up to 8 med-small (1.5- 2 inch long) silkworms EACH per day split over 2 meals EACH.
If he's not coming up to a shed.
It's likely you have not enough UVA (and UVB), because your UV light is too far away , not rated at least 10%UVB , has a mesh top between the light and the beardie (this will result less apetite).
Also if he's too cool in his tank he'll not be as hungry as he'll be metabolizing food more slowly - check the warm and basking spot temperatures.
The light cycle may also have an impact , if the lights are on for less than 14 hr per day , he will not have sufficient time to warm and bask and take in sufficient UVA and UVB.
