I have chronic diarrhea that comes and goes, but it is very difficult to overcome...i've had a recent colonoscopy, all fine...possibly stress-related?

Possibly: Loose stools are one way that the body can express stress. Have you considered tai chi, yoga, meditation, deep breathing exercises or acupuncture to reduce stress? Take care.

Probiotics: Try probiotics (i.e. Yogurt) or a gluten free diet. If part of your prep included antibiotics, this can change the bacterial flora in your intestines. If you are dairy intolerant, there are probiotic supplements available in the majority of pharmacies, including target. If part of your stress includes drinking coffee or smoking, i would try decreasing one or both of those as well.