Hello,

Has anyone had constant diarrhea lasting over three weeks?

no - You should call doctor's office or at least your NUT - You had your surgery in Sept? you should able to eat regular foods? do you eat anything with Fiber? - like Beans? Fiber helps both ways - with diarrhea and with constipation. Also, are you lactose intolerant? I found out I was after surgery. I even had problems with whey Protein and was glad when I could actually eat most of my protein instead of rely on shakes.

Drink plenty of fluids and throw in something with electrolytes to help with dehydration issues - because you are probably at least a little dehydrated. But you really need to call your NUT as soon as you can and if he/she is not available an on call nurse.