Welcome to HealingWell.com! You will find a wealth of knowledge, experience, and advice here, I hope it all serves you well.
Sorry to hear you've been having trouble. While the rest of us can give opinions and suggestions, your doctor should really hear about your colon-cancer fears and the changes in your stool output. Of course feel free to express yourself here, but your doctor is the only one who can put your fears to rest :)
You said that you've been to the hospital, but were they telling you that you have gastroenteritis (stomach flu) or gastritis (inflammation of the lining of the tummy)? No problem about the spelling errors, just want to make sure :)
Did the doctors at the ER prescribe you anything? Normally they'd tell you to make an appointment with your Primary Care Physician. Have you done that? If not, I would say that it's your first step on the road to recovery and/or answers :)