Hi,
Lower back pain can sometimes be associated with Urinary Tract Infections (UTI), Kidney Infections, and various other health issues. Sometimes bacteria (usually E. Coli) from loose stool or diarrhea can find it's way to the urethra and can travel into the urinary tract causing an infection. If left untreated, the infection can cause pain and eventually extreme illness. You should probably be examined by a doctor soon, especially if the pain persists or becomes worse, and if other symptoms emerge. Take Care :)