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Black colored stools and constipation
( unable to pass motion freely) are common side effects of using Iron tablets. You need not worry about them and need not stop taking iron pills. Taking plenty of fiber rich diet like green leafy vegetables, fresh fruits especially citrus fruits will help you in passing motion freely.
and delivery are physically and mentally demanding states. As you have mentioned you had lot of blood loss during delivery.
are the reasons for you feeling tired and drained. Taking good diet will help you get over it. Iron rich diet is preferable. Jaggery, peanuts, pistachio, dry fruits, green leafy vegetables and chicken or mutton liver are good sources of iron.
Try to have at least 2 eggs a day, fish at least twice a week and meat once a week. Take plenty of fresh fruits and vegetables.
Good diet alone can do wonders and makes you feel better. Meanwhile dont feel too worried and enjoy the motherhood. I hope you would be back to norm in no time.