Sorry to read that you are not feeling well. Most people here advise to get a colostomy to confirm what is going on inside. If it is something they can deal with on the spot they will, if not they will do a biopsy to see what is going on to come up with a treatment plan.
Lastly, even if things are ok, the best way to know is to have the colonoscopy. Evidence matters in the proper diagnosis of what is going on with you.
I wish you luck in uncovering the good and bad and moving toward a successful solution.
D/H 47 years old, 10/2014, Stage IV M/CRC, nodes 12/15, para-aortic, 5 cm sigmoid resection, positive Virchow. KRAS mut, MSS, Highly Differentiated, Lynch Neg, 5FU/LV and Avastin 1 YR (Oxi for 5 months) NED 05/2015, Zeloda/Bev since 01/2016. 02/2019 recurrence para-nodes, back to 5FU/LV Oxy/Bev, pending genetic results. "...Perseverance is not a long race; it is many short races one after the other."-Walter Elliot