After i orgasm i get a burny lower back pain. im 18 and a female. any ideas?

Here are some ...: What you described is how your body responds to sexual excitement. Is such experience new or lifelong to you? If lifelong, that is how and what you're; if new / recent, seek pro-evaluation and counseling to see if there is something happening in the pelvis. But, largely, there would be not much that could be done and it could be related with muscle discomfort from orgasm-related tension.