Your symptoms and mine are very similar. I have been dealing with IBS-D for over 25 years. It sounds like you are doing the right things diet-wise. Has your doctor given you any meds? Right now I am taking Donnatal, which helps the cramping significantly. It does make me very groggy, so I only take it if I am staying at home. I have found that less cramping results in less D... and less queasiness and nausea. I started out with Bentyl, but it ceased to be effective after a few years. I was then put on Levsin, but I fund the side effects bothered me more than a flare up did. Many people find relief from Calcium, although that did not work for me. Immodium is another thing that has given a lot of people relief.
Take care, and enjoy your good days