If i test positive for a rubella infection, can that be effectively treated with a vaccine?

No: A vaccine can only prevent, not treat, rubella. However, a "positive test" usually just indicates that one is already immune, either due to prior infection, or more commonly, prior vaccination. Fortunately, rubella is rare in the developed world due to near-universal vaccination of infants.

RUBELLA: Rubella is a viral disease caused by rubella virus and antibiotics are not effective against it.The disease has to take its natural course. I suppose you are referring to a person who has rubella rash and has positive IgM titer to confirm the diagnosis.But if you only have positive titer of IgG antibodies that means you are immune to rubela and will not get it again.