Coughing After Exercise?

Hello Answerers of Yahoo Answers! My problem is that I'm not quite sure if this is normal. I'm thirteen years old, and overweight. Well, at my school during gym, we sometimes have to jog for only about 5 minutes around the gym. I usually only jog for about 1 minute. Then I stop and start walking, because I just can keep jogging. Every time, once I stop, I can barely breathe. I usually end up coughing and wheezing, breathing heavily and gasping for air. Because of my weight, I usually just assume this is because of my lack of exercise. However, I now have a new theory. Is it possible that my lungs are just weak? My parents smoke, about a pack a day. Also, my sister just began smoking. She smokes everyday, while driving me to school (about a 30 minute ride). I know that secondhand smokers (those who breathe in the air around a smoker) can have worse affects than the smoker themselves.

My question is: Is it normal for an overweight person to gasp for breath after exercise? Or do you think this could be related to secondhand smoking, and weak lungs? Or could it be the mix of both of these things?

Thank you so much for answering! I really appreciate it! :)