After running, I could not breathe for an hour. Why?

Hi doctor,

I am an 18 year old female. My height is 5.6 ft and I weigh about 120 pounds. I live in a city where we do not have much air pollution. I have no records of medical problems except a few years back I had some mild acid reflux. I believe it was reflux, since it went away after using Gaviscon. But, my general physician did not diagnose me. About two months ago, after I went for a very fast run I felt like I could not breathe for an hour. Since then, I have been having the feeling of not being able to get enough air when I take deep breaths. I also have been constantly clearing my throat due to mucus in the back of my throat. I have been experiencing some burn in my upper abdomen. It is not so severe and it goes away with some Gaviscon. I feel nauseous when I feel the burning. I am worrying myself by thinking that there is something wrong with my heart or my lungs. If you could help me that would be great. Thank you.