Well, if parasites are a suspected problem, you shouldn't be taking Imodium because it doesn't allow your system to be "flushed" - it can make the problem worse in the long-run. If you go through testing and it's found that you are parasite-free, Imodium isn't a bad idea, but before you take it long term you might want to try other methods, like Keri suggested - fiber supplements like Citrucel and calcium citrate (make sure it's not calcium with magnesium added, as magnesium can be a bowel stimulant and cause diarrhea). What sort of testing have you had for your diarrhea?
Some people swear by probiotics - I take them too. I think they're definitely a good idea if you've been on antibiotics recently or have an infection.