This sounds like
painfulPainful menstrual periods trigger points in the pelvic floor muscles. Locate a qualified pelvic floor physical therapist. One who does myofascial release, not the "kegel only" kind. THey may be able to diagnose your pelvic muscle trigger points, and cure them with manual release techniques. I assume you have had the workup including negative pregnancy test, negative cervical cultures, negative urine culture, and no pelvic masses.
PLease let us know how this turns out.
Dr. hoyte