I have the flu, I think... medicine question?

You can't know for sure that you have the flu unless you are tested for the flu. If you do have the flu, you have a limited amount of time to take the flu pill, which will reduce the duration of the flu. So you should check the symptoms of flu and then go to the doctor. While you're at it, check the symptoms of scarlet fever. Sore throat and a rash are two of the symptoms.