Worried? whats happening?

I'm 15 year old girl who has sufferd from anxitey, panic, depression for about 3 years now and im on a antidepresaant called sertraline. I'm always very panicky and paranoid about my health and always asume something is wrong, I had a blood test a month or so ago and a EKG and they both came back fine apart from i was a little low in iron so my doctor prescribed some iron tablets and i finished the course. My heart always feels like it's racing at least twice a day I get that skipping beat feeling, i can always feel my heart beating and even the simple tasks like walking up the stairs have me a little out of breath sometimes... I'm not over weight, I'm curvy and weigh about 10 stone.. if thats normal? Sometimes i get a little shaky in my hands and a weakish feeling and sometimes achey pain in my left hand or arm, diabetes does run in my family too but I'm really worried and panicking because I keep thinking i might have a heart attack or somethingbbecause its my left side, really scared and panicky please help? My left hand feels a little week and my forearm kinda aches :(