Hi,
One way is to try using soluble fibre supplements like Equate (walmart brand) or metamucil (if you haven't already). Fibre is naturally contained in food and help bulk up stools.
If the soluble fibre supplements on their own doesn't work - Have you ever tried taking calcium supplements? Powdered calcium is much stronger. However, be very careful, because calcium is very strong. It can turn normal into extremely hard stools and it can turn constipation in to a colon ripping rock-like thing.
Powdered calcium tastes awful, but works even better.
So, try taking calcium with your meals. Remember to drink plenty of water/fluids.
You should also remember to use plain white yogourt to help repopulate your intestines with the useful bacteria that help digestion. They get washed out with diarrhea, and will need replenishing.
There'll be more information on this topic on this site if you do some searches too.
If the above techniques all fail, there is another good method - but I'll reserve that for later.
Cheers, Raju.