hello thank you for trusting HCM dear most common cause for stomach pain and diarrhoea is acute gastroenteritis it maybe due viral or bacterial in origin. other causes like food poisoning which may present vomiting and nausea with abdominal pain with or without loose motion. chrons disease or malobsorption is rare cases for it drink plenty of water and ors.check for serum electrolytes because you already have foot cramps. if symptoms not improved please consult your doctor he will examine and treat you accordingly. I think I answered to your question if you have more questions feel free to ask. take care