Chest pain, lasts 30sec-1min comes&goes. athlete but feels much deeper than muscular/skeletal.focused on left side.sometimes radiates to upper back.

Chest pain: You will need to see a doctor licensed in the US for specific diagnosis and advice. You will likely need examination. Here is some general patient information on possible causes. http://patient.info/health/chest-pain-leaflet

Multiple Causes: Chest pain can be a symptom of heart disease but may be may other things such as esophageal spasms, great vessel disease, respiratory disorders (asthma, COPD, bronchitis, infections), and muscle problems to name a few. It really depends on the clinical situation and other symptoms you may be having. it is very unlikely that at 18 it is serious but should see a doctor to get more information.