Hello. You should go back to the doctor and ask him/her if they think a medication such as Nystatin would be something to treat the mouth symptoms that your son has. Also it is very important to make sure that he is drinking enough so that he does not become dehydrated. It is probably very painful for him so I would avoid any warm or hot liquids and give him cold things. The cold might help with the pain as well. I hope this helps you.