Diarrhea constipation gas swollen stomach = colon cancer?

Not always. Although change in bowel habits is a strong indicator of colon cancer, it can signify other things as well, like irritable bowel syndrome, or gallbladder issue, i.e. Stones. Your'e young for colon cancer, and gallbladder issues. So it is likely that the source of this lies elsewhere, like your diet. You should see your doctor for tests like occult blood test, etc to be sure and for diet help.