I have racing heartbeats, headaches and breathlessness at times. What could be the cause?

Hello doctor,

I need your help. I have seen many doctors about the symptoms that I am having. Several years ago, I would have these little episodes with my heart where for about five to ten seconds, my heart would race extremely fast when I say remarkably, I mean, within 5 seconds, it would beat 15 times. That would happen every once in a while. That eventually stopped and turned into episodes where it would skip beats, and I would feel like I needed air, get an immediate headache, have chest pain and pressure, feel fatigued, and many other symptoms. I saw many cardiologists, and they did many tests, and they could only find the palpitations, which they said was expected, but they could never really answer why I was getting these symptoms with the palpitations. The last cardiologist I saw said that my heart issues were caused by my hyperthyroidism, which was Graves Disease. I had the radioactive iodine done about six months ago. My symptoms should have stopped, but they did not. I am very sensitive to caffeine, and if I have a little bit, it will make my heart start having the issues even worse than when I do not have caffeine. I know there is something wrong with my heart, but I cannot find a cardiologist that will listen and fix the problem. The most I was given was heart medication which did not work. Please help me tell me you know what is going on and can fix it. Thank you.