Recurring utis, lower left back pain under rib cage, high white blood cell count in urine, nausea, weakness. Causes?

Pyelonephritis. It sounds like you have pyelonephritis/ renal infection. You could have infected kidney stones or an obstructing ureteral stone. You could have vessico-ureteral reflux or a large post void bladder residual. I would recommend that you see a urologist and get a renal/bladder ultrasound and voiding cysto-urethrogram. Good luck.