What are symptoms of colon cancer? I ve been having changes in bowel elimination lately ~2 months with periods of very loose bowels (diarrhea) and then nothing for a day or two. My last colonoscopy was good and I was told that I did not need to take another one (I am 78). I am taking 250mg of Magnesium daily. Would that cause a problem? Also have been eating lots of fruit like peaches and nectarines. I thought that was the problem, but even when not eating these fruits the problem persist. I feel great except for feeling tired and I attribute that to my age.