Change what you eat. Some foods make you more sleepy than others. Foods with sugar or white flour (as opposed to whole grains) are often the problem. Foods such as turkey which contain tryptophan are well known to cause sleepiness too. Other foods with lean protein and low carbohydrate are more likely to keep you alert. Start keeping a log of what you eat and how sleepy you are afterwards.
Try some changes. 1. Eat about half stomach solid food, quarter stomach liquids in the mddile( warm) and keep rest empty. Small luch and dinner and heavy breakfast. 2. Improve your sleep and fatigue if one has, exercise moderately. 3. Avoid high carb diet, sodas, chocholate, 4. Eat high fiber diet and have regular bowel movement if not. 5.Try to sleep from 10pm to 6am and adjust sleep hygiene if needed.