Does colon cancer always cause diarrhea, thin stools, or constipation?

I ask this because I have been going a bit more lately (around twice a day instead of just once), though on some days I'll go only once, and very rarely none at all. But my stool size has been relatively normal, and I haven't had any diarrhea/mucus stool for quite some time. I guess I'm worried because my bowel habits go through mild changes periodically, and there's no set time for when I go, though they're usually after lunch and dinner. I've also been getting some cramping, sometimes severe, predominantly right on my lower-left abdomen (sometimes mid or even right side). Most of the time I need to defecate a little while after the pain sets in, and it seems to get a little better during and mildly begins to subside after I'm dome. I just worry because this is a recent development for me and it's worrisome. I haven't lost weight, in fact I've gained, and I do have an appetite. I also usually get a little nauseated after eating food (usually, the greasier the worse). I noticed little maroon dots on my stool, but I havent seen any streaks and these dots aren't too consistent. I'm only 18 so it cant be from just getting older. And one more thing, it tends to worsen when I focus on it, but it begins before that. Oh, and sometimes I feel really tired, but other times I feel wide awake, and my Dr. doesn't think I have anemia. I worry because I hear colon cancer may not cause symptoms until late.

I'll vote with the anxiety. With me, Metamucil worked as a great regulator and source of fiber as well. However, as the other poster said, signs of blood in the stool are never welcome and the spots you notice are the ones to be concerned about. i.e. bright red is not that much of a worry but dark/brown are. If you haven't mentioned this to your doc you should and ask him what he thinks about a colonoscopy - there are other things besides cancer that can occur in the colon.

The size, shape, thinness or thickness of your stools and the frequency of your bowel movements have nothing to do with colon cancer.
There is no reason to believe you have colon cancer and there are several far more likely causes for your symptoms.
You should tell your mother. She will know if you need to see a doctor.

I would advise a colonoscopy, i don't know how old you are but my boss's son was 24 when he got colon cancer. Caught in time, he's o.k.
Can't hurt and it's not that uncomfortable, i had two.
you heard wrong, any sign of bloody stool or spots f blood should be checked out

I think you have anxiety and it's causing irritable bowel syndrome.