First....Don't give up! Never give up! The pain is REAL:, it is not just in your head. Heart issues can happen at any age. It took me some years before that finaly said I have AFIB. So keep on them. Can you tell me where you are located? How far away are you from Austin, TX?
NEXT" Track your blood pressure and pulse. Keep a chart so you can show the doctors. For example, I take mine first thing every morning. There was a time when I took my BP five times a day. Any time you are having problems, take and record your BP and also take your glucose reading if you can. Like someone else said, get all your medical records reguarding this issue and keep them handy. Keep a log going. Write down every time you have an issue..
I know this is very frustrating for you. Mostly it's the feeling you are being dismissed. I went through the same thing. I too did all the heart tests they could think of. It just took time and finding the right doctor.
I recently had a Watchman device put in my heart. Took me a very long time to get it done. What was the final deciding factor was after they did a Nuclear stress test on me and it showed some abnormalities. I may also end up needing a stent put in. Will have yet another cath done after the watchman healing process is done.
I wish you well and hope you get some answers soon. As before, don't ever give up. Best of luck to you.