When you describe "greasy yellow" stools as being "bile", you are correct. You're not absorbing fats well, and after 2 full months of symptoms, it's time to visit your doctor. Could be gallbladder, could be pancreas, could be a many different things. It's normal to feel drained and tired after having diarrhea. You lose lots of fluids and electrolytes can get out of whack, so keep up the fluids - water or gatorade, not coffee, tea, or colas, that sort of thing. Do you have any other symptoms aside from the bowel changes? Any pain or cramping? Any changes in your diet or new medications?
It's probably not anything serious, but since this has gone on for a while now, it sure wouldn't be out of line to ask your doc about
your symptoms. Hope you get to feeling better soon.