You have my sympathies L-R. Check it out with the doc.
I had similar symptoms and followed the common sense advice of fruit, fibre, fluids - didn't make much difference, in fact bran and milk was downright unpleasant. Later got a tentative diagnosis of irritable bowel syndrome - stress will out somewhere if we're adept at suppressing it. All goes back to the dim recesses of the brain where peristalsis is controlled, and no amount of fibre helps. Try a stress free break see if the symptoms go.
Another possibility is a lack of fluid retained in the gut to help things along. A mate was prescribed 'Fybogel' for this, it seemed to work for him.