Welcome to Healthcare Magic forum.
After going through the description provided by you, I am of an impression that it might be a heartburn
or any myocardial abnormality as it is been radiating to your left arm. But as you are 16 yrs old, it is rare to see in your age group. It would be also better to rule out any history of injury
But before going for an examination, I would suggest you to consume cold
milk or water to see if the pain reduces or not. If it doesnt reduce it would be better to get examined by a Physician at the earliest. He might ask you to get an ECG and few Blood and Urine tests.
Hope this answers helps you.