Where are you located? Mostly it is the wrong time of the year for brumation... could he be impacted?? Try a little unsweetened applesauce with a drop or two of olive oil in it...give him a few bites and see if that doesn't help him go poo,,,also, a nice warm
bath and gently massage his tummy from under his arms down towards his vent.
Also, loose the infrared light..he doesnt need heat at night unless the room where you keep him gets below 65 degrees. If so, then get a ceramic heat emmiter. What are you measuring your temps with? You need a digital therm. with a probe, or a temp gun. He should have a basking temp of 95 - 110, hot side, 85 - 95 , and a cool side of 75 - 85.
Also, he needs to be eating more .. you should be offering him feeder insects daily along with the greens and veggies. Also, are you using supplements, as in calcium and vitamin powder??