Welcome to health care magic! I have gone through your question and from my clinical experience I can say that the probiotics, though otherwise useful , sometimes may cause gas and bloating in abdomen, this thing in turn increase the nausea. It is not that giving probiotics is wrong but preffrably we need to see the antibiotics we are choosing. the metronidazole, a good antibiotic has high propensity to cause altered taste and nausea, and similar is with ciprofloxacin. It is a usual presentation after someone is treated for gastroenteritis, you please start taking a combination of Esmoperazole / rabiperazole with domperidone twice a day , half an hour before meals for a week and be fit!!( However this should have been given in the beginning of treatment itself.) taking ondansetron was also a right step, but this will not help in treating cause of nausea which the above medicine will. Nothing to worry about, go for light diet and avoid spicy and oily stuff for few days. Hope the reply is helpful Feel free to ask more questions Dr. Manisha Gopal.