I'm 16 and think I have bowel cancer, please help!

First of all, you probably don't have colon cancer since it's uncommon for teenagers, and the biggest and most worrisome symptoms include blood in stool along with weight loss. There are other symptoms you could experience like nausea or abdominal pain, but those are the most worrisome ones. On and off constipation and changes in stool can be linked to a handful of other abdominal issues, such as a poor diet to irritable bowel disease. Seriously, I never knew how much stuff could cause this until I did some research. If you are very scared, talk to your parents and ask to see your doctor because you're worried about your recent bowel movements and stools. 

I agree with Emily.  There are many things that could be causing your symptoms of which, at your age, bowel cancer is probably the least likely.  You should see your GP, though, because you obviously have concerns and it is worth tracking down what the cause of your symptoms might be in case some action is required.  Telling people not to worry when they are having health concerns is not usually productive because worrying is a natural reaction.  However, worry is one of the things that can cause problems with the digestive system!  This is another reason why a visit to the GP is a good idea, just to put your mind at rest.

John you don't seem to have any of the red flags I'm not a professional but I would say it's probably not something serious but see a doctor and maybe he can ease your mind also colon cancer is very rare in younger people