Should I still be worried after all these tests? Heart palpitations, dizziness, !

I am a thirteen year old male, and about 6 months ago I started getting chest pains, palpitations and a fast heart rate... some of these were also with dizziness. After about a month of symptoms, I went to the doctor. He said he believes it's not a heart issue or anything dangerous, but to make sure he would get tests done. I had a blood test, EKG, ultrasound of my heart, halter 24 hour monitor, and stress test. He also of course has listened to my heart and done blood pressure tests. All tests were completely normal. I have been to the ER from being worried over this. I have left school, and many other things, because of these feelings. I tell myself nothing is wrong, but at the same time I still worry. My main fear is sudden collapsing of athletes especially, because of heart problems. I have been an athlete for many years but ever since the first symptoms, I haven't played sports competitively or in a fast paced way. I know I am out of my regular fitness level due to this. Could being out of shape and being stressed over this cause palpitations and a fast heart rate? I admit my habits aren't great as far as sleep, water amounts I drink, food I eat, and stress levels go, but could this cause anything? I am extremely worried, and any answers would help me.
Thanks, Tj