I think I have MRSA but can't see a doctor until tomorrow, what should I do overnight?

MRSA. If you think you have mrsa, keep the area clean, apply warm compresses to the area to try to soften it and, hopefully, get some pus out of it, then see your doctor.
How do you know. Not all bacteria are mrsa, if you have no abvious infection or sign of an infection, there is no need to panic, you can simply see you doctor, when ever possible and have a nasal culture for mrsa; however, if you have high fever, an abscess, a spreading redness on your skin and you are feeling terribly sick, you should go to the nearest emergency department.