Chest pains on the left side of chest

I am a 17 year old male and i been having chest pains since septmeber 2007 and was admitted to the hospitol on dec 9th 2007 due to chest pains Once in the hospitol i went throught alot of test such as an ekg,Xray of the lungs and a cat scan of the chest with a ultrasound of the legs and they found nothing I went to the cardiologist And they gave me an ultrasound of my heart and found nothing but a leaky heart valve...im not sure which valvue or how leaky but that is what i been told..my chest pains occur MOSTLY on the left With rare occurence On the right When i get a pain on the chest i noticed it happens depending on my posture...like for example i was sitting on the train today and i had a pain so sharp it scared me it occured on the left followed by my body getting hot and left arm in pain These Pains Only last for a few seconds then go away.Most pains occur while sitting in weird positions such as laying against something.....doctors say it may be a problem with the chest wall but i cant walk around with my head held high just thinking it can be a problem with the chest wall

But before i had any chest pain i was in Boxing for fitness And one person got a really good hit In my stomach which had left a bruise ..My family has no history of any heart condition but these chest pains scare me alot can anyone help me??