20 years old w/ possible colon cancer

Hi everyone!

I'm a 20-year old male, and I went to the doctor today because of rectal bleeding that's been occurring for a little under 4 years now on and off, a few times a year. There was never any pain associated with the bleeding, and the blood was always a relatively dark liquid.
She performed a rectal exam, and came up with nothing, and referred me to a GI doctor for a colonoscopy, but I can't get an appt until late November. Which leaves me in limbo for several months, and I'm already worried.
Here's what my doctor was asking about:
I've had the aforementioned bloody stools for several years. I generally have dull abdominal pain, usually at the end of the day, regardless of what I eat. I am constantly tired no matter how much sleep I get, always falling dozing even in important situations like class, driving, etc. She brought up the fact that my eyes get red often. Finally, diarrhea is a weekly occurrence for me. Also, my great uncle died of colon cancer at the age of 40.
I think that's about it. I'm just really worried sick, and I guess my question is, how likely is it that I should prepare for the worst?