I have this sometimes - I ended up being diagnosed with acid reflux and esophagitis which was exacerbated by stress, haha. So basically, I would eat something fatty/greasy/unhealthy, and I already have a genetic predisposition to have acid reflux fairly badly (dad and mom have digestive issues including acid reflux), and then I'd be spending my afternoon with funky pain in my upper left abdomen. I thought I had the weirdest things (and most terrifying) but I ended up being diagnosed after getting an endoscopy and bloodwork done to rule other things out. Now I occasionally take 15 mg of Prevacid and it clears the issue right up until the next time I stress/eat poorly. Evaluate your diet and when the pain occurs, this may give you some clues as to what is going on.