Anxiety makes you over-analyze yourself so every twitch, ouch, hot, cold or numb sensation seems to be a clue for you to follow up on to figure what is wrong. Since you don't accept the science that has determined twice that you do not have a heart problem, your anxiety is having a fine time playing with your body making you go into overdrive with fear - it is normal high anxiety suffering and lots of people including myself have gone through it. Just as you have done, we headed to the ER after the "symptoms" of chest pains, twitches, sweats etc. got to us. We got our ECG tests saying no problems just as you have done.
The road to peace is when you accept the science and stop trying to diagnose your "mystery" ailment which the docs say you do not have. Once you accept that then the pains will disappear or at least be reduced, and you will not be feeding Mr. Anxiety. You are not on that road. Not everyone can get relaxed and accept the diagnosis but many have found ways, such as going to therapy to get some suggestions. Here is a CNN article about an anxiety sufferer (it is the fourth one from the top) who tried everything, but so far anxiety will not give him a break.
http://www.medhelp.org/user_journals/list/676326?personal_page_id=890501
The road to misery is where you try to figure what is wrong with your body because you know the pain is real and the pain means you have an ailment but the docs don't understand. It will not stop as long as you keep believing something is wrong, because it would be a frightening situation for any 25 year old if you really did have a heart condition. You are on that road.