i need to know whats worng with my stomache

I am 14 years old and I have had a problem with my stomache for about 3 years and no doctor seems to know what it is. I get sharp stabbing pains in my stomache its usually the lower left side of my stomache but it spreads to different areas. i dont drink but i do smoke cigarettes. i would really like to know what it is. I just want some information so i can look into it. i need some kind of lead to something that it could be. Tweet