Good question... sorry I don't have an answer. But I do have to disagree with the suggestion that you get an upper endoscopy. Your symptoms don't seem like they'd be related to anything going on in the upper GI tract, so it probably is either the hernias or a little IBS.
You may need to get the ol' scope down the throat. It can be anything from plain uncomfortable to downright excrutiating(similar to alien experiments) you may need to ask for seditives before the procedure. It may determine your problem, as it takes a sample of the small intestine as well. A general FACT is that if a stomache produces too much acid, it will make your food digest quickly and like battery acid, will disolve your food to liquid in a hurry, which in turn, runs through the system. Good Luck