Any time you make a big change in your eating patterns, it can result in constipation OR diarrhea. Different people react different ways. Fortunately, the remedy for both is the same...more fiber. You can try plain psyllium husks in water, but I've never been able to get past the taste or texture of that stuff. Ground flax is a great way to add fiber to your diet and get some very healthy Omega 3 fatty acids in the bargain. There are also fiber caplets that you can take.
The good news is that it's usually only a temporary problem until your body readjusts to your new way of eating and will usually clear up on its own in a week or two. If not...try adding more fiber.
HTH!