After doing Cardiovascular Physical Activity such as running, my heart starts to pound extremely hard and I feel like im not getting enough air. Im only 17 and im not overweight (5'10 and 155 pounds) and i have normal body fat composition. I am somewhat active as well. However, i can barely run 1/3 a mile before my heart starts pounding and if i push past it, after a while it starts to be painful. I eat well and i dont have a family history of heart disease or anything. i do have allergies though and i live in a pretty polluted city. My resources are kind of limited, I live outside of the US in the Armed Forces Pacific. Im just trying to figure out if this is normal and im just in bad cardivascular shape or could it be something more?