If you are over 40 years old, and have never had a colonoscopy, you should see your gastroenterologist.
No. Diarrhea after eating is usually not serious. It can be due to irritable bowel syndrome or lactose intolerance. First, try a lactose-free diet (no cheese, ice cream, cottage cheese, sour cream, white salad dressing such as ranch, and only lactose-free milk, such as lactaid, soy or almond milk). If the diarrhea does not go away, you can try peppermint oil before meals. If no relief, see your doctor.