hi i am a 15 yearl old gurl i am a really outgoin teen i have fun a lot. im always active but i havea problem. that a few months ago everytime i have fun or do somthing really active it makes my heart super speed up. really fast to the point that i feel really breathless and get headaches and sumtimes my left should hurts a little. i dont think is that of a normal thing to happen. anything i do even when its not as active makes my heart beat speed up. and lately i been having trouble breathing. what do you guys think i have? or what should i do? i went to the dr. and told them about it. but didnt took me serious. they said that to not worry about it. that it was good. but i dont know i dont think its good for my age. or i dont kno what do you guys think? is it normal?