What causes flank pain and how to treat it?

Flank pain is pain felt in either the right or left back side of your body below the last rib and above the pelvic rim. It can be caused a kidney problem, like a kidney stone or infection; muscle strain or spasm; or an irritated nerve. Sometimes pain in the right flank is due to a gallstone, and pain in the left flank can be due to pancreatitis or a problem with the spleen. Treating the underlying problem helps relieve the pain.