Cancer of sigmoid colon - is this hard to diagnose? I have so many symptoms but nothing showing on test results

Hi all. 
is cancer of the Simonides colon hard to diagnosis. My blood tests are clear my fit tests are clear. 
my stools are very thin. I’m constipated chronically and have to take laxatives and laxido plus enima. Ct scan shows swollen inflammation on left side of colon plus small lung nodules left side. 
my tummy is distended and full wind. This first started in august 24 very severe constipation had colonoscopy it was clear. I’m living on laxatives I’m tired and burning pains in left side tummy. I cannot pass a stool without laxatives I feel my gut has stopped working ? Anyone else similar. I’m booked for simodocopy in 2 weeks x