colon cancer symptoms ?

I first want to say that I have health anxiety and tend to think I have all kinds of things, I am trying to overcome it but it causes alot of sleepless nights. I was pregnant when it started. I am 36 years old with no family history of colon cancer or personal history of cancer. While I was pregnant I started having alternating bouts of diarrhea and then normal then constipation. I started seeing a lot of mucus in the stool, sometimes white sometimes yellow. I then had the baby 4 months ago and after the birth of the baby noticed a lot of bright red bleeding on my stool and it stung a little to have a bm, then it stopped bleeding after a few weeks and I counted it up to hemorrhoids from pregnancy, but the alternating constipation, normal, then diarrhea continues. I also get gassy and there is a lot of mucus. The stools seem to look different too. I am also having abdominal cramps at time on the left side and they sometimes move around. My stomach was hurting bad the other night so I went to the ER. they did blood work, a abdominal cat scan without contrast and a abdominal xray. She said everything was completely normal. My blood levels were fine, the cat scan showed no obstruction, inflammation, kidney stones or diverticulitis. Now here is the question, what is the chance of these being colon cancer? If I had an advanced cancer would they have seen anything on the cat scan or xray or blood work at all? Can any of these tests help me be less worried at all? She said it sounded like IBS and intestinal spasms. I do tend to make more of symptoms then there is but am really losing sleep over this could someone help me out with this. Are these test any indicator? Would ADVANCED cancer shown up in any of these tests? thank you. No one wants to do a colonoscopy on a 36 year old with no family history.