Thanks for posting your query.
Do you have acidic belching/ abdominal bloating/ excessive flatulence/ epigastric pain/ fever/ hemetemesis?
Your symptoms suggest that you are suffering from acute gastroenteritis
And improvement after taking O2 suggest the same.
But presence of black color stool is not a good sign.
Black color stool may be due to medicines, persistent constipation
and bleeding from UGI tract.
You should consult with physician and gastro-physician and should go for endoscopy
You should continue your prescribed medicines along with proton pump
Dr. Mayank Bhargava