Hello, I Am Diagnosed With Diverticulitis And All My Life

Hello, I am diagnosed with diverticulitis and all my life have had stomach "aches". I had a test done several years ago that showed a spastic colon and stomach. My question is, I am extremely tired all the time and have red streaks on my face that run down each side of my nose, down under my chin. I have heard that fatigue is an underlying symptom of cancer. This concerns me because of the fatigue and that I am being watched closely with blood tests for cancer. Would a blood test show definite signs of possible cancer?