Eating small amount of food even when I am hungry makes me feel very uncomfortably full. You should I continue to eat, it is painful.?

PEPTIC ULCER. The feeling of early satiety (feeling full) maybe a sign of a peptic (stomach) ulcer. Some warning signs are dizziness, 'dark stools' or vomiting 'brown coffee grounds' (all signs of bleeding ulcer). These warning signs are an emergency so get to the er right away. General treatment: avoid caffeine, alcohol, and smoking and several months of 'acid blocking meds' e.g. Prilosec, Prevacid (lansoprazole) or others.
Stomach pain. Stomach pain may be due to several things: ulcers (but usually improved with food intake); acid reflux; stomach mass. You should see your pcp or a gastroenterologist (gi specialist) for thorough examination to determine the cause.