Thanks for posting your query.
Is this black colored stool very foul smelling and watery in nature?
With the available described symptoms, there appears to be high possibility of melena.
Blood leaked in upper gastrointestinal tract gets converted to black color due to acid in stomach.
You should remain in touch with the treating doctor and should go for endoscopy
He should also go for complete blood count
, renal function test and serum electrolytes.
Hydration should be maintained by taking appropriate intravenous fluids.
may be needed to to correct blood loss.
Dr. Mayank Bhargava