I have not used this personally, but I wanted to pass on this recommendation that I just found on another forum and that is apparently really helping other IBS-D sufferers:
Have you tried calcium carbonate to help with your diarrhoea? It is an over-the-counter mineral supplement (not to be confused with calcium citrate, which is better for the bones, but doesn't help diarrhoea). You do need to check the contents. Many contain magnesium. Avoid any supplements containing magnesium, as this can make things worse. However if you find calcium carbonate combined with vitamin D and other minerals, you should be OK. (Also watch out for lactose, if you are lactose intolerant).
Do check with your Chemist or doctor that it will not interact with any medication you are currently taking.
Hope this helps you,