There are all kinds of reasons they could come back positive - hemorrhoids would be teh most likely one. Other possibilities are fissures, infections, polyps, ulcerative colitis, diverticulitis, Crohn's or yes, cancer. The last is probably unlikely if you had a colonography two years ago that showed nothing as I think it usually takes longer than that for cancer to develop from precancerous polyps, but it is still possible. 

I think overall 10% of positive FIT tests are cancer and it would probably be lower in your case both because this is a long-standing issue and becaue of the previous colonograph showing nothing to worry about.

Age also makes a difference. The younger you are, the less likely colon cancer is, though again there is no age at which it is impossible.

The FIT test only tests for blood in the stool. It doesn't mean that cancer is likely, just that they have to check because it is one of many possibilities.

Thankyou, that helps.  I guess I’m just worried and will feel better after the colonoscopy.