As long as your humidity levels stay at or above 50%, there's nothing wrong with the heat lamp, and if your house is cold like you say, you may need to keep it.

If you have humidity trouble though, I'd recommend a second heat pad. Heating pads should be applied to the bottom of the tank, not the side since heat rises. Flexwatt heat tape is the best kind of under tank heat around. You can buy it by the foot, or in sections already wired. When you have a thermostat, make sure both heating pads are the same kind and size if you plug them both into the same t-stat.. you can't have two different kinds of heater on the same thermostat.