This could be the most frequent gastrointestinal complain, a irritable bowel syndrome (alternating forms of stool, and the sense of not completing the bowel movement, are very characteristic for this syndrome; nausea is not common for this syndrome, but, you may have other intestinal problems, like acid reflux, or gastritis, at the same time).
Because, its symptoms aren't specific you may still want to get check for colon cancer.
Best wishes!