What should I do...

It's pretty cold in my room and I just got a BP 2 days ago and the only heating source I have for her is a under the tank heating pad. Should I get an infared lamp for her?

Your thermostat (hopefully you have one) should not let the temps go below what you have it set for.

A light fixture would not hurt and would help keep your temps up,or you could buy a space heater and use that to heat your room up. The space heater will keep you and your snake warm :).

^ ^ x 2

You need a thermostat hooked up to your heating pad with a temp probe on top of the glass over the heating pad in order to maintain the proper temps as the ambient temperature in the room gets colder or warmer.

I would NOT suggest a heating lamp as they make it very hard to maintain proper humidity levels.

I agree with all of them, but I do use heating lamps because my house can be drafty (especially after all the snow and ice storms!!), and I have no trouble with humidity. I use Zoo Med Eco Earth substrate and it retains moisture very well. I'd definitely invest in better heating though, no one likes a cold snake!

Heat lamps make humidity very hard to control. I would insulate 3 sides of the glass, cover 7/8 of the top, and add a 2nd UTH. Set the 2nd UTH about 10* cooler than the warm side heater.