Happy Valentines Day......it sounds like your parents did the right thing in taking you to the E,R, but this may be something so simple it would surprise you. If you are sitting at your computer for long period of time that would explain the neck pain, stomach cramping, and chest pain...no movement for extended periods of time. You need to get in the habit if you are on the computer of practicing correct ergonomics and change your position at least every 30 mintutes. Your stomach is sitting in the exact same position as well as your neck back and chest..try raising your hands over your head , wiggle your fingers when you do it....get up and bend over and stretch,walk to the kitchen for a glass of water. The chances of anything happening to your heart at your age is pretty darn isolated especially if all of your tests came out okay. Stress could also cause alot of your symtoms,,,,pressure at school, pressure w. your friends, a bad relationship, pressure from your parents....look at it for what it is my friend. You haven't described really anything that is heart related as in electrical activity misfiring, rapid pulse, any of it. I would modify the time i spent on the computer...good luck to you and don't worry if there was something wrong the E,R, would have known it and treated it...do process of elimination in your life...eliminate what is stressing you out...
It is good you had medical attention.
You say you get relief from getting up and walking around. Do you get any other exercise? I think stress, anxiety (caused by the pain - pain adds to anxiety) and tight muscles may be the problem.
Talk with your parents and look on the web or talk to a physical education teacher about exercises that will relieve tight chest and kneck muscles.
Good luck, you should be alright - but see a doctor again if you don't get better, that's my thinking.
Coronary artery spasm? (e.g. Prinzmetal)