What causes pain on left side that radiants to the back?

Watch for fever.: So hard to answer a question like that on here as there can be many causes and some can be serious. Kidney stones or swelling, muscle spasm, spleen and colon problems can all give left side and back pain. See your physician if it doesnt resolve on its own or if it has been present for more than a few days. Chills or fevers would be other reasons to go see your doctor right away.