What can i do for this pain left side of chest and back?

See a doctor: There are many potential causes of chest pain, from musculoskeletal to respiratory to cardiac/heart, among others. Without a complete history & exam, it's impossible to determine the cause of your chest pain. You should make an appointment w/ your primary physician to determine what testing or treatment is needed. IF IT'S NEW CHEST PAIN WITH EXERTION, YOU SHOULD GO TO THE CLOSEST ER IMMEDIATELY

May be rib issues: including muscle spasms causing them to tighten from trauma or postural issues, specific muscle spasms. However, you should be examined to rule out spleen, stomach and even cardiac concerns. I do not see male/female on your question above, but remember women can have completely different signs of cardiac issues as men and this should always be ruled out first.