Started having intermittent pain in lower abdomen, back and side, mostly left, sometimes right. Tests for infection and stones negative. Help!?

Did you start w/ ur. Internist? A good internist should be able to ask more questions and perform an exam to try to narrow down possible causes. As described, the possibilities are broad including spinal, muscular, intestinal (gas, diverticulitis, atypical appendicitis, other), prostate/testic/epidydimis (if male), ovarian/uterine (if female), kidney stone (can be missed by ultrasound), bladder, arterial, & more.