Hi, Welcome to health care magic, I have read your query and understand the concern regarding your father since he had been operated as stated by you. From his symptoms, it seem to be having acute infective diarrhea considering loose stools with upper stomach pain. Or it can also be related to irritable bowel syndorm after the operation,he suffers loos stools after eating anything. So,before starting medications,it would be advisable to undergo routine blood counts,ESR,urine and stool tests with serum electrolytes especially sodium and potassium. Generally,it might take 48 to 72 hours to subside loose motions following appropriate antibiotics and other symptomatic medications. Therefore,he would require 1) Ofloxacin with ornidazole antibiotic for at least 4 to 5 days with 2) Antiemetic (ondasetron) if you feel nausea or vomiting, 3) Antispasmodics (dicyclomine) for abdominal pain or discomfort twice or thrice daily. 4) prebiotics and probiotics (sporolac-DS) with racecadotril sachets with water 3 to 4 times a day to restore intestinal bacterial flora. 5) Take plenty of water with fruit juices (especially coconut water) to maintain fluid and electrolyte balance in body. 6) Avoid heavy diet and take light or liquid diet for minimum 3 to 5 days. 7) Lopamide (Loperamide hydrochloride) can be taken 2 to 3 times a day which actually slows the movement of the intestines. This allows water to be absorbed from the stool, so the stool becomes more firm. All above medications are available over the counter except antibiotic and it might take 2 to 3 days to control watery motions. If symptoms persist then see his operating doctor for further examination. Hope this detailed information will be helpful. Regards