Your CT scan was not a waste. They were probably looking for a renal or ureteral stone if it was done without contrast.
CT is not the best diagnostic modality for colorectal cancer, especially if the mass is small or inside the bowel lumen. Some cancers can be seen on CT as a mass, stricture (apple core lesion), or a "filling defect" if oral contrast reaches that part of the bowel. Inflammation can be seen with both benign causes (diverticulitis, colitis, etc) and with cancer. Many cancers (including my 5 cm mass) will not be visible on CT, even with IV contrast. It also matters if you have IV only or oral contrast only or both. Each imaging or diagnostic modality has its strengths and weaknesses. We have all had bloodwork, colonoscopy, and CT. Some will also have had US, EUS, MRI, and PET. Each has a specific role to play.
Without IV contrast, evaluation of the liver is limited and small lesions can be missed. The word lesion is used to describe an abnormal finding. Because many things can look the same, they will be called lesions until it is known or suspected that they are cancer (primary or metastasis) or something else (abscess, cyst, benign liver tumor, etc.). It's just a way of saying "abnormal thing" in that organ.
There are many other things besides cancer that can cause the symptoms you described. Take it step by step, and try not to worry (easier said than done, I know).
Stage IIA rectosigmoid CC (T3N0M0)
Dx 6/5/17 @age 41, mom to 5 & 2yo girls
Workup: c-scope, EUS, rectal MRI, CT C/A/P
AdenoCA 5.5cm, WHO Grade 2, 0/22 LN, no distant mets
CEA 1.9 (6/5/17), 0.8 (2/28/18)
No lymphovasc/perineural invasion, clear margins
MSI intact, OncotypeDx RS 7
Lap sig colectomy 6/23/17, no ileo/colostomy
Genetics counseling negative for mutations, 4 VUS
Xeloda monotherapy 8/13/17-1/22/18
PET/CT 3/21/18 NED