Anyone have a clue of whats going on?

Alright so far i've been having Chest Pains (Left Side sometimes Middle and other pains like Shoulder, Neck, Jaw, Hands (Both hands) and stuff for like 2 months) Doctor told me i had Costochondritis BTW i'm only 13 and i was wondering two things first off Does anyone know why my left hand has a sore kind of feeling and my palm was hurting for a while but stopped (Ever since i had Costo i kinda stopped exercising alot just every now and then and i kinda eat a little bad now and then but my second question would my Arteries be Bad as im only 13 Years old 98 -100 Pounds and Skinny PS.. I'm not sure if my Chest pains and stuff come from bad Posture as i used to Sit on the PC ALOT and i do Play Games hours at a time just laying across my bed on my side, Anyone have any ideas? ALSO my chest pains seems to just Dissapear when im in School hanging out with my friends like i feel it less then when i feel it at home I really dont know what is up with that. Arms kinda sore feeling like i pulled something. Also i went to the Doctor already Had an EKG a Chest XRay and Blood Test (Blood test i did at home since my dad is a Doctor) And they said Everything was Fine.