My sister is experiencing stabbing pain in her lower back on the left side, just above the hip. She says it is not "back" related. Pain comes and goes in 15-20 minute increments and has become more frequent over the last several weeks. She has been diagnosed with IBS. She eats a very healthy diet and works out regularly (cardio, strength, yoga, etc.). Can you give me any sort of idea as to what might be going on?