I am sorry to hear that you are starting to feel bad! It is certainly possible that your symptoms are related to exposure to the flu or another virus, especially if other people at your school are having similar symptoms.
Unfortunately, there is no way to prevent the illness
from coming on if you have already been exposed and infected with the virus. There are certainly some things you can do at home to calm your stomach, however. These would include avoiding any spicy or irritating foods (including caffeine and alcohol) as well as smoking. You can also eat bland foods, like crackers, soups, and the like, which should not upset your stomach.
Even though most of the time the virus will run its course without any medical intervention, your doctor
can definitely prescribe you some medications to reduce the symptoms and get you feeling better. They can also answer any additional questions you might have about your symptoms. Good luck, and see your doctor soon!