I have had this problem since I was little (about 8ish years old) and have had a 24 hour heart monitor in the past which showed no irregularity.
Whenever I run, ascend steep stairs, go uphill or lift heavy objects etc I instantly get chest pain which locate on the left side of my chest, under my collarbone area, above my nipple, this causes strong palpitations and strong arm pain in my left arm, it usually subsides after about a min or two but certain pains persist for a little while longer until I relax. What I find more odd is that every time it happens I feel a need to yawn and yawning often subsides the pain.
I'm 6'5 tall so I'm not ruling out muscle or skeletal related problems. My diet is anything I want these days as persistent knee injuries and the chest pain when exercising I haven't been excising but I have had is since I was little so I wouldn't put it down to my diet.
I had a stomach operation regarding reflux when I was about 1, not sure if that is connected and I have also found out I am seasonal asthmatic (summer related).
I am not exactly expected a full diagnosis over the internet but just some advice as to what it could be would be good.