Thanks for your question.
Basically this is concerning since this means that you are losing iron or not taking an adequate diet containing iron. Please investigate the cause for the iron deficiency.
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We cannot rule out internal bleeding based on the response to the treatment. It just means that you are having iron deficiency. For knowing the cause your doctor may recommend investigations based on your symptoms.
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If it was a significant bleed they may be dark, however in cases of chronic minor bleeding there would be no change color.
More commonly this may be due to hemorrhoids or due to an ulcer. However malignancy may also be the cause.
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