im 19 years old about 5ft 4 ... could i have colon cancer? no family history of bowel cancer that i know of my mum had breast cancer and my nan had cancer(not sure which) . i have very dark stools and i fear dark blood a fair amount on the tissue after every stool im not sure about blood on the stool, im very very moody and tired. i have started to suffer from constipation and diarreah for the last 2 months or so mainly constipation and when i do have a stool i sometimes struggle and i dont feel as though ive finished . i also have a very high fat and high callorie diet but weigh just under 7st . please help!