Why do I feel so stuffed after eating so little.?

Enzymes. Even the thought of eating starts the release of digestive juices (enzymes). Stretching the stomach with food starts enzymes in the small bowel that cause fullness. This is usually a good thing and prevents over-eating. What amount is "eating so little? ".
May have. And ulcer in your stomach or swelling from inflammation or a tumor that limits gastric emptying and gives you early satiety, the feeling of fullness after very little food. Please see a gastroenterologis.