Plain yogurt/ Acidophilus

The good bacteria in plain yogurt helps fight yeast and yogurt can be used both internally and externally. BUT, be sure you buy plain, unsweetened yogurt. Since sugar feeds yeast, this is a crucial point. You can also use Acidophilus to feed your body good bacteria.

For a topical treatment, you can also dip a tampon in plain yogurt and insert it into your vagina or simply rub some on the outside. However, that leaving it on for a prolonged period tends to have the opposite effect. It seems that once it has done its job, it is best to wipe it off or you will feel itchier due to the moisture.   
Taking Acidophilus supplements will also help, because it helps replenish the good bacteria that will help you fight the yeast infection.