Go see a doctor, and get a kidney function test! It could be as simple as intestinal gas pockets, or it could be a kidney stone stuck in your left ureter (hose from the kidney to the bladder). Two people close to me have had bad kidney stones, and also gas problems, and they say the pain can be equally intense, and hard to tell the difference. One thing for sure, if you get a fever, GO NOW! That means the kidneys could be getting infected due to the blockage, and that can be fatal if not treated quickly. And don't let any numbskull tell you that you're too young for kidney stones. My wife started getting them at 17.
Charles