Hi thanks for asking question. Omeprazole and zantac are same group of drug in reducing acid secretion... You have not mentioned reason for using these drug.For constipation or diarrhea it is not used. Just now your diarrhea could be by simple gastroenteritis if you have taken out side food.Antibiotic needed for it.... Maintain hydration with ORS and water. For few days soft diet taken.Do not take heavy fatty food. And ya if you gave alternate constipation and diarrhea with abdominal discomfort it could be irritable bowel syndrome like condition... Avoid stress as it will aggravate it.... If stil cause not clear USG done for further work up...if needed endoscopy might done. Take care...