Supplement with magnesium. That helps with regularity and a couple of hundred other bodily functions. Don't take a full dose right off the bat. Try to ramp up slowly because it can having your running to the bathroom every time you turn around if you go from nothing to full dose.
Magnesium Oxide is the most commonly available and it is the least expensive by far (and I take it) but it is the least absorbed. Google around for better types.
Fat is far superior to fiber for regularity too. Fat greases the skids, so to speak, and fiber works by abrading the lining of the colon bursting the cells along the wall.