magnesium, magnesium, magnesium.
prior to giving them up, i ate buckets of grains and legumes, so had giant bm's all the time. when i eliminated them, i went from low-fat to high-fat at the same time, so frankly everything was a bit too loose down there for awhile. ack.
once my body got adjusted i was having serious constipation issues. one vacation i thought i would die because i was so backed up. i started taking magnesium daily and have never had a problem since.
agree though, with others about healing your gut. DO NOT!!!! DO NOT!!!! DO NOT!!!!!!! add more fiber in any form. do not take any kind of fiber powder. stay away from raw and cruciferous veg. start having bone broth, even 2x per day. work with fermented foods like kimchee and sauerkraut. have good yogurt if you tolerate dairy.
be patient. this will take awhile.
i'd be a vegetarian if bacon grew on trees.