What does it mean when you're done eating and then have to poop right away?

Postprandial urgency: The need to have a bowel movement immediately after eating is often due to spasm of the colon. It is not necessarily a normal urge. Sometimes it is a sign of irritable bowel syndrome. Before seeing a doctor, it is often useful to increase fiber and fluid intake, and perhaps even try a fiber supplement, such as Metamucil. If this doesn't work after 3 to 4 weeks, see your doctor. Good luck.