Hi. Thanks for your query. Noted the history and understood your concerns. Sudden change of diet to something ideal will cause many of the problems as your gastrointestinal system is not ready for such changes many a times. Hence it can cause Gastrointestinal bleeding, bloating, cramps, GERD, nausea, vomiting, weight changes and so on. Black stool and in the vomiting is indicative of an intestinal bleeding and hence I would advise you the following: Send the stool for tests including that for occult blood for three consecutive days to get a proper diagnosis. Upper GI Endoscopy and Colonoscopy may be needed. If the bleeding source is fund urgent care will be needed. Stop anything new and revert back to your normal usual diet which should be soft and bland. Take a PPI like Omeprazole, antacid when on empty stomach. Further management as per the findings.