What is the temperature in the warm side? do you have something regulating the heater? those get hotter than a BP needs and on top you have a light too. It is probably too hot and thats why he doesnt go in the "warm" side. I started just like you too. I dont use the lamp anymore. They get light cycle just from ambient light (sun light through your window) in your room.

95 should be the most hot. 93 or so recomended. Even at 95 they will leave the warm side alot.