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Dark , green stools may result from presence of bile, blood, or food ( licorice, ingestion of lead, iron, bismuth ). You need stool analysis and liver
function test that will clarify. Additionally you need Endoscopy
to examine your stomach and duodenum
( in case of erosion there can be present small amount of blood that can cause dark coloration of your stools ). In such case you may seek Gastroenterologist consultation and request above mentioned tests that will help understand your condition, find cause and accordingly will be more easy choose treatment.
I wish you good luck and speedy recovery,
Hope this helps and I have answered your query.