Alas I have had the same experience. I tried the Primal Diet for 4 months and was completely into it but my IBS symptoms were killing me and I lost a lot of weight. You might try instead the Low FODMAP diet. look on this site in the forums under 'Diet'. It helped me tremendously
(Sign In - IBS Self Help and Support Group Forums - IBSgroup.org).
These days I eat mostly complex carbohydrates (vegetables) with a little brown rice and quinoa, and salmon once a week.