EKG and echocardiogram

I am 15 years old male. I am extremely worried that something might be wrong with my heart. I had an EKG done by a cardiologist and it was negative like 6 months ago. I had an EKG and an echocardiogram done 2 months ago and it was also negative according to the cardiologis nothing seemed wrong and then he was going to send my results to my general doctor. Since then i am so worried that something is wrong because like in 2 months can things change like all of a sudden get a heart problem. I play basketball and am worried because on saturday the coach is going to make us run for an hour. like an hour of running is kind of worrying to me because like i get dizzy and my legs spasms after like 10 minutes of running fast. Like we do defensive stances which make my legs twitch but then stops, but when we run and i put any sort of muscle pressure on it it starts to twitch and my legs feel numb. I also feel dizzy. I do have anxiety and am nervous 24/7. I play basketball in high school. I am 5'8" and weigh like 115 pounds.
Is this an irratinional fear that i will die or faint?