How do I know if I have asthma?

I do varsity soccer, varisty track, varisty cross country and travel soccer. Once at camp last year when we were back packing I had shortness of breath and was wissing. And last week at soccer I had the same thing happen. It was only the second time this has even happened. I can run 6 miles non stop with no problem in breath or cramps. It wasn't too hot or I wasn't over heated or dehydrated when this happened. So I don't know what it was. Cause I can run fine and have no problems. When this happened my counselor was like you might have asthma and my coach said the same thing. But how is that possible? If I can do some many things fine, but randomly this happens?