“Should I be worried?”

I’m a 17 year old female who’s been experiencing palpitations and tachycardia for some months now. I’ve had many EKGs and been to the ER many times for them (even though there were no additional symptoms) they gave me an IV and sent me home. A lot of the time my resting heart rate is about 100-150 even. I don’t have shortness of breath or chest pain but considering this is nowhere near a normal heart rate for my age I am a little worried. The ER workers and the ambulance drivers never seemed to be too concerned about it so my parental guardian but I'm very scared that one of these days it’s going to result in cardiac arrest.