Try this:
Also I am not medically qualified nor am I a nutritionist but what I do if I start feeling ill is eat some ginger (crystallised is fine) and also try to get a couple of cloves of garlic in food, or minced into some bouillon, and also, drink a couple of teaspoonfuls of any kind of vinegar in warm water (through a straw so it won’t corrode your teeth). Red wine vinegar or apple cider vinegar for choice, but I used to use ordinary malt vinegar as well. (Edit to add, I space these apart, all three at once would be too much.)
Your entire body chemistry and spiritual balance may differ from mine so I can’t just say “hell yeah do this” but maybe research the ideas.
Pray (telepathically send a petition to) the god Thoth for insight as to how to prevent illness and for success and protection for your exams:
Finally, go to a mirror, look yourself in the eyes, and state “I give you pemission to be sick after these exams, but not yet!”
Don’t try to do anything spooky, or go into trance, just do it like a conversation with yourself, then walk away.