i agree with Ace. it looks like he/she might of fallen and gotten a small wound, bruising the ribs, went un-noticed for possible a short period of time and became infected. or maybe it is some other type of skin infection allowing the skin and muscle around it to become very tender and bruise easily. if you are not 100% sure about what it is by the end of a day or two, i would go to the vet.
No I am using a 50 watt heat lamp and the tropical UVB bulb. It's a 2 foot bulb but it is spread over two cages. I recently acquired her and assumed she was hurt during transport.