Traveler, are you taking a good probiotic? If not, please try that.
Also, sweeteners called "sugar alcohols" -- names that end in "-itol," like sorbitol, xylitol, etc., can cause something like what you are experiencing. They did with me. They are frequently found in so-called "healthy" foods in health food stores and are touted as less problematic than ordinary non-sugar sweeteners. They are not. I was getting sorbitol in sugar-free gum I was chewing, and it really wreaked havoc on my GI tract.
Also, when I was younger, I had a spell of almost exactly what you are experiencing, except that mine was coupled with nausea. I was finally diagnosed with what they called back then "spastic colon" which meant that instead of normal peristaltic action of the intestine to pass food along, my colon was going into a spasm every time I would try to eat, so the minute the food hit my stomach I'd have a violent reaction.
They gave me a drug to slow down the colon and stop the spasms. It worked wonderfully -- it was called librax, and there was another one whose name I cannot recall for nausea. Anyway, turns out most of it was caused by stress (and of course the affliction itself causes a tremendous amount of stress). Eventually I was able to be OK without the medicine, though I still have occasional flareups. You should ask your doctor about this drug, if you haven't tried it already.
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