I have severe pains in my upper left side of my chest. how c an i know the difference between gas pains or something more serious??

You can't.: chest pains can be difficult to diagnose, even for experienced physicians. If you have new onset of chest pain, no matter how innocuous it may seem, you should make an appointment to see your doctor. If your pain last for more than a few minutes and has not yet been evaluated, you might even consider a trip to the emergency room. The most important thing is not to ignore it. Good luck.