I would echo the recommendation about improving your gut flora. Your elimination is basically stuff not being used by your body. Many folks have reported less content once going Paleo -- because they were eating less non-useable stuff. But if you are only going every few days with the help of Magnesium, it sounds like you don't have enough of the good bacteria in your gut.

Try a probiotic (you may have to experiment to find one that gives you what you are missing), eat fermented foods. You might want to read up on leaky gut syndrome or SIBO to see if any of that might apply to you. It sounds like your problem is higher up the chain. . .

DAmn! I read somewhere that diarrhea could be a result of LACK of magnesium - so I've been supplementing with it. No wonder it hasn't worked!

Twenty years ago, I had a colon specialist who was a professor at a medical school operate on me for hemorrhoids. He told me most digestive disorders were the result of constipation. He told me if people had more fiber in their diet--he would have almost no patients. The modern diet just doesn't have enough fiber. There are two types of dietary fiber--soluble fiber and insoluble. In the palo diet most foods have both types of fiber. But if you must use a supplement use something like metamucil. The skins on apples, potatoes, etc will give u insoluble fiber. That coupled with milk of magnesia on the rare occasion you do get constipated will keep you regular. Also the old 8 glasses of water a day rule is TRUE.