Hi I Am 50 I Have Thickening Of The Lining

Hi I am 50 I have thickening of the lining and I am hypothyroid. I am tired all the time and have gained 17 pounds in the last 5 months. I do sit for my job 9 hours a day. I have blood in my stool, tired all the time.
What could be going on now with the blood in my stool? I had a colonoscopy in 2012 everything looked good.