Irregular bowel movements, cramps that I couldn't attribute to what I ate, inexplicable fatigue. Eventually it was a bright red blood in stool which made me force my doctor to take it seriously.
Be careful with this, or at least scaring/stressing yourself with this. Fresh (bright red) blood in stool is 95% of the time hemorrhoids. Most colon cancers will present with old (very dark red, or black) blood in stool.
My doctors have been like that too. I have to pull their teeth when I want some sort of screening done or want to see a specialist, but because I'm relatively fit, healthy, with no family history of anything "bad", they say my risk of things is low.
I don't care. I just want peace of mind. Cost isn't even an issue, I would be willing to pay a decent sum to get regular screenings so I'm not blindsided with some stage 4 diagnosis down the road.
BTW The American Cancer Society recommends colonoscopy screenings starting at age 45 routinely now if there are not other indicators to start even earlier.
Is it doctors, or is it medical administrations reluctant to deal with "selling" your insurance provider on covering you for a service?
At least in the US, I've found that if you're paying cash up-front, you can shop around for what you want, without referrals, and without this kind of hesitation.