Weak heart beat and tiring easily

[TeenMale16]

Hi, im 16 and have got myself in a state over my heart again. I had an ECG q few months ago and all was good but being referred to a specialist for an echo. Recently i have noticed i was getting out of breath easily and tiring easily. My heart doesnt seem to be pumping as hard as a week ago and i keep thinking i have had a silent heart attack. It isnt beating irregularly as far as i can tell and maintains a good 60-70 bpm. But why is my heart beating weak. Can anyone help?

[TeenMale16]

THinking about it now. A few days ago i had a dull ache in my left arm and now my fingers on my left hand are tingling. Im so scared to go to sleep as i feel as if i wont wake up. I know its unlikely but i think it is a silent heart attack.