I second the advice for a PT-trained fitter. It sounds like you saw a good fitter, but he is probably still not equipped to handle your specific muscle imbalances and needs. For example, he may see that you're flexible and can handle a more aggressive setup, but maybe that isn't the best thing. Maybe it is, but you just need to learn how to sit properly on the bike such that you don't aggravate the imbalance in your pelvis. Maybe a tilt in the nose of the saddle one way or the other could help you. There are some fitting services offered at more medical type facilities (where they may have physicians and/or PTs on hand, and where you can get fitness testing done). Now the fitters there may not be as good as the one you went to, but they may understand what's going on with your biomechanics more, giving you some valuable information of how you should be trying to sit.