It's been 3 weeks , i am feeling full after eating anything like breakfast or lunch. I usually don't eat big or small meals, i eat medium sized meals . But when i eat very small meal , i feel ok. As i am underweight i can't eat small meal everyday otherwise i'll lose weight easily. I feel fullness after 1-2 hours of eating. I also feel gassy sometimes. Inspite of eating healthy foods, drinking 3 litres of water, doing yoga and sleeping 7 hours , these issues are happening. Can you tell me what could be the cause?