Reasons behind Weakness or sleepiness after meals are high carbohydrate diet or insulin resistance. When you take a high carbohydrate diet or when you have insulin resistance there is increase surge of insulin due to which your body goes into relative hypoglycaemia state which makes you sleepy and dull.
Regarding supplements it is always better to take supplements as adviced by the physician and that which targets specific
vitamin deficiencies.
Next Steps
1. Eat small meals more frequently or meals high is vegetables, salads, protein and low in carbohydrates.
2. Get blood investigations such as RBS,
Hba1c done to know your blood glucose levels.
3. Consult a endocrinologist.