I have reviewed your question.. It seems like your body is depleted of the essential nutrients post delivery. As you know during pregnancy body sacrifices its own resources to the well being of the baby. It would be better if you have calcium rich food in your diet like milk and milk products, leafy vegetables, millets and cereals. There can be vitamin D deficiency post delivery which can also contribute to your weakness. So you should check your Vitamin D levels in blood. You should make sure that your hemoglobin level is normal and if low you should increase intake of iron rich food. Last but not least have a check on your thyroid hormone levels, as hypothyroidism can cause this level of lethargy and sleepiness. Try to have a healthy and complete diet. Thank you.