Most commonly seen vaginally, secondary to a change in the natural
flora.
Antibiotics,
intercourse, change in
hormone levels and diabetes can predispose to yeast infection.
In the really immune-depressed (AIDS or steroid users), you can see skin and oral yeast infections (thrush).
If the discharge keeps coming back and is a little on the green side, maybe it is your protozoan pal, trichomonas.