What could cause lower back pain lower abdomen pain?

An ulcer, gastritis, There are several possibilities including disorders of the GI system, kidney or renal system, cardiovascular system & the reproductive system - ulcers, pancreatitis, infections, aneurysms, endometriosis , ovarian cysts, diverticulitis, pelvic inflammatory disease, ectopic pregnancy, kidney stones, infarcted intestines, volvulus, intussusception, tumors & adhesions are just a few possibilities.