I have had some constipation too, and I think it's actually because of increased fiber. I think because of the diet change, I need to add even more water than 8 glasses a day, because the increased fiber, especially the higher ratio in my diet, needs more water to move things through. I think most people think a high fiber diet automatically would make one more "regular," but sometimes Metamucil is given to make liquid stools more solid. I think in my case at least, that my body isn't used to all this fiber. Increasing my water is helping. (accept I still have to pee too often!)
Another helpful hint: if prune juice doesn't do it for you, try heating it in the microwave. Hot prune juice works great, especially if you haven't eaten for a couple hours before taking it!
Teresa