What Causes Severe Lower Back Pain After Masturbation?

I am female, 29 years old and virgin. I get severe lower back pains after masturbating and the pain continues for weeks. It has made me avoid masturbating at all , the frequency has decreased to once in a 2 moths but each time i do it, I get sever pains. In my MRI nerve pain has been diagnosed but i am unable to walk, bend or any other physical activity.