hey!
i sort of know how you feel..
i get palpitations where it feels my heart has skipped a beat and then races.
also sometimes get a sharpish pain or a sort of pressure feeling.
not to be complainin or anythin lol.
iv been to a n e twice over sharp pains, i got a chest x ray and everything was normal. iv had a whole bunch of ecgs and even a 7 day monitor. and still they tell me theres nothing wrong..
they said it was anxiety.
i know what you mean bout the age thing im 17 and completely freaked bout these heart things. iv avoided sports and stopped running because im scared something will happen.
iv stopped caffeine too. dont drink coke or anything and yet i still get them =[
iv never had an ultrasound but id say its pretty unlikely you have heart disease especially if your healthy and exercise.
could be a wee bit of arrythmia which is no harm at all! just a wee bit of extra electrical signals in the heart.
or could just be anxiety it can do a whole bunch of stuff to your body.
anyway hope this helps!!