Hi Hopelessanxiety,
I am sorry you are having this pain. Sandee is correct there are numerous thing this pain could be. Because you are so young it is not more apt to be a muscle or possible GERD, (gastrointestinal reflux disease). However one should never R/O (rule out) cardiac issues.
I would consult with my doc to see what could be causing this. I hope you are soon feeling better. Keep us posted and take care, Tuck
How long has this been going on?
What other health issues do you have, any heart problems?
There is really too many causes and without more info I can not say what your experiencing is.