Why wont the doctor prescribe me anything to help with pain after a rhizotomy?

Hard to Say. You need to speak with the doctor to find out what his/her stance is. Some doctors write pain meds some don't. If that is their policy you may need to discuss your options with your pcp.
Consider approach. Asking them for non-narcotics. I find that if you offer to comply with what they are offering for 24 hours, and simply state you have tried it (without being agressive) they will increase the power of the medicines used until you find relief. They don't want you to hurt. But if you come accross as drug seeking that isnt justified, they will be reluctant to participate. Submit to their advice key.