Hi. Thanks for your query. Noted the history of consuming sandwich with boiled potatoes yesterday evening, got uneasy and vomited three times, Stomach cramps developed with loose stools. Your short and specific history is suggestive of an intestinal infection and hence I would advise you the following: Get the stool and blood checked. Consult your Physician for clinical evaluation, examination and getting started on appropriate antibiotic, metronidazole, probiotics and activated charcoal.This will solve your Problem. Stop eating anything that is stale and preserved. You should have strictly home-made food. Treated water orally in plenty and along with Electrolytes.