What Causes Pain In Lower Left Quadrant?

I occasionally get this pain lower left quadrant when i breathe. I have had normal bowel movements, no diahrrea, no vomiting, a little nausea but mostly just this nagging pain. It is a dull ache until I take a deep breath and then it is a sharp stabbing pain in my left side. Most people have described these symptoms as gas pains but I figured after a few hours and with some medication gas would have subsided by now. I feel well other than this pain in my left side. My bowel movements continue to be regular, at least once a day ...some mild nausea but nothing more than that, just the sharp pain when breathing deeply. What could be the cause of such pain?