[JerryMaffz]

You say you have a heat mat set to a thermostat and a UV Tube.
Perhaps your tortoise isn't getting enough heat to digest it's food.
I would ditch both and invest in a combined heat/UV lamp, though you could run a heat only lamp alongside the UV tube. The heat lamp should be set at a height so that you get a reading of around 32deg at tort level. I leave my lamp on for around 10 hours a day.
Another possibility for the weight loss/ lack of appetite could be an internal blockage. I would think that the wood chip may be the obvious cause of this. Though this is less likely with the high fibre diet described, it is worth checking out.