Brief Answer:
Upper GI bleed or iron supplements most likely in your case ma'am

Detailed Answer:
Hello ma'am and welcome.

Thank you for writing to us.

I have gone through your query with diligence and would like you to know that I am here to help. Based on the information provided in the medications tried box, I am suspecting a bleed, but let me list the two most likely causes for the black colour stool in your case:

+An upper gastrointestinal (GI) tract bleed: When there is a bleed from the upper GI, the blood mixes with the stool (that is yet to form) and so it results in black colour stool (also called melena)

+Iron supplement cause black colour stools

As you were feeling nauseous, which is a symptom of conditions like peptic ulcers, etc; I strongly suspect an upper GI bleed which will require investigations like an upper GI endoscopy and an elaborate blood profile. I hope you find my response both helpful and informative. Please do not hesitate to write back to me for any further clarifications, I am always here to help.

Best wishes.

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