I would say it's pretty unlikely to be cancer. At your age, something like ulcerative colitis or Crohn's would be much more likely, even if it is something serious.

I had a colonoscopy last August due to rectal bleeding, weight loss, some loose stools (maybe once or twice a week) and trapped wind and the consultant told me that at my age (40, at the time), cancer would be the least likely of the possibilities and that I would be "the unluckiest person in the world" if it turned out to be that. Given that you are little more than half my age and it doesn't sound like you've had any bleeding, the odds of cancer in your case are likely to be even lower.

I know it's scary and that "very unlikely" isn't that much consolation as it still leaves margin for error, but i would say the odds against cancer are very much in your favour.