upper left chest pain

As far back as i can remember i've always had chest pains, the doc's said there wasn't anything wrong with me and after ekg test and all that they'd send me on my way, now that i'm 24 i'm getting a little concernedsince the last time i saw a doctor he told me it might be snm or sumthing like that, he said it was some kinda heart and lung disease. My symptoms include sharp pains on the top left side of my chest, during anytime of the day and weither i am doing an activity or not, placing pressure on the area by pushing on it with my hands helps relieve the pain a little and so does pounding on the spot....now I do drink a lot of coke a cola and eat a lot of chips and I did smoke but I am trying to quit and have been smoke free for the last month, I also eat a lot of healthy foods like vegitables and milk and fruit and my job helps keep me in pretty good shape...I was just wondering if you could lend me a hint on what is wrong with me since all the doctors i have talked to or that have tested me have said nothing is wrong even though i know there has to be sumthin wrong.

thnx

HighC