Uy, I feel you, that's a common complaint this late in pregnancy, pero since it's more intense than usual para sa'yo, mas better na i-check mo na with your OB just to be safe! At 36 weeks, your body is really preparing for labor, and back and pelvic pain can be normal, pero kung sudden ang intensity or may other symptoms, better safe than sorry talaga. One of my mum friends had similar sharp pain and it turned out she needed monitoring, so don't hesitate to call your doctor or go in for a check-up, they'll ease your mind agad!