Tell the principal and she will probably talk to the nurse or even fire her, if this has been the case for other students in your school. I think the nurse underestimated the pain or probably thought that as long as it doesn't affect the other kids, you can go to school. Many teachers that are mean only follow what they're given to teach or do and dismiss everything else, and complain about how much work it is for them. So, you can either tell somebody or deal with it. Nothing much to do about it, really.