Bera, your doc probably wants to do the scope because it's really the best way to diagnose inflammatory bowel disease and other problems. They take a few biopsies, usually, throughout the colon. I've had a total of four scopings done this year - two upper and two lower (this is not typical! Most only have one!). All of them were easy as pie. Drink the stuff the night before (tastes bad - but it's over quickly), hang out on the pot all night, wake up early, get an IV, and go off to la-la land for a few minutes. I always asked for light anesthesia and even if I was slightly awake during the procedure, I was never aware of any of it, or didn't care what they were doing. Your eyes might be open but you're really not thinking about anything, not in pain, not scared; all your senses are completely dulled. Then when you wake up, it's all over. Feel a bit groggy and go home and lie around like a sloth on your couch!
It's better to just get it done if you've never had one and you're experiencing bowel problems.
As far as the diarrhea goes, how often are you going? Some people have found success with fiber supplements; others with Imodium; others with probiotics; others with nothing. Don't freak out necessarily if nothing seems to work. You will adjust to this problem slowly (no, it's not fair, but it's what inevitably happens). Eat easy foods, nothing weird. Bananas and rice work pretty well. That's until you get your scope, which will rule out the major offenders, and you can go from there.
Good luck girl - we've all been there, or continue to be there!