Intensity. Low back pain the is getting longer and more intense is always suspicious of endometriosis. A limited amount of pain that precedes your menses by a day or two and is relieved by itself by day two of your flow is often normal. Don't tough it out. If you can take an NSAID (ibuprofen or Naproxen sodium) right when the pain starts and decrease the length and pain. Consult your gynecologist.