I agree with Arie. Most likely it's gas or constipation (have you been eating things with sugar alcohols in them, by chance?), but it it continues to bother you or gets worse, go see your doctor. There are no organs that I'm aware of to the left of your stomach, but there is a bend in your colon there and it can cause some discomfort if a gas pocket or fecal matter is having trouble passing through that spot.