Chest pain during exercising?

I used to be very active up until I was about 19, and now I am 21 and although I may do something active every once and a while I don't work out that much. Yesterday I worked out for about 30 minutes and broke a sweat and had to stop because I was having a mild chest pain. I am a female. It was in-between my left breast and my clavicle. It wasn't severe but discomforting. I did feel short of breath..but that wasn't the main reason why I wanted to stop exercising I worried about the mild pain. I think I have experienced this before when exercising in the past few years. Could this be  aortic valve regurgitation? Or could it just be stress induced? I also have a small form of asthma, could that cause this mild pain? Eventually it went away after about an hour of resting, but today when I was walking to class I notice very mildly I felt the pain again. I don't have insurance or much money...that is why I am posting this question here. Thanks for any help.....

[tamara869]

I forgot to add....I had an EKG done when I was 19 for heart palpitations...it came back normal...said it was just anxiety induced.  Maybe once a month my heart skips a beat...it used to be more often but I don't experience it as often as I did a year ago.