What to do if i have pain under my rib cage on my left side that goes around to my left shoulder/neck?

See your Doctor: Cardiac issues will have to be ruled out first, anginal equivalents may include symptoms like this, your doctor will then check for shingles and/or mechnical pain that can be reproduced in the office. The next step would be to consider, bruised or contused rib, without fracture (periostitis). More rare would be a subcostal neuritis which is usually very challenging to treat but there options.