Jodie, don't let anyone tell you it's all in your head if you are feeling pain, including doctors. That is enormously disrespectful. Just because doctors cannot locate the source of the pain doesn't mean that it doesn't exist or isn't legitmate. Doctor's don't know everything; that is why they are called "practicing physicians". There are many instances of doctors being wrong. Be relentless to find answers Jodie...and don't allow anyone to disrespect you by insinuating "you're crazy".
That being said, I read your first post and it sounds exactly like something I have dealt with. Sometimes if I stretch my arms out, or move in an odd position, I get that excruciating cramping feeling in my chest cavity that is hard to pinpoint and it feels like it's going to "pop" or burst. I have two options; either breathe through it so it "twists" and pops which is extrordinarily painful, or breathe shallowly and eventually it will go away.
I have been dealing with this since I was your age (I'm almost double your age now, assuming you are 16) and I have also had EKG's and many other tests done on my system (for other reasons...not for this particular one) and I have been found to be in perfect cardiac health.
Someone explained this pain to me once as a charley horse in the chest; or a lack of oxygen in a muscle. When you move your muscles in one way or another it cuts off the circulation (and oxygen levels) in those cells causing these cramps.
Although I do not have pains in my arms or neck or jaw, this chest pain sounds pretty similar to yours.
I have not thought twice about it for many years.
I hope this helps ease your mind a little...good luck...