If you are sexually active it may be your partner. keeping yourself clean has alot to do with yeast infections. In my first marriage my husband wouldn't take a bath maybe once a week and that's were mine were coming from. I told him if he couldn't keep himself clean he wasn't getting sex from me. This was very embarassing for me, it may not be for the men but it is for the woman. If this isn't it I suggest going to another doc for a second oppinion to make sure there is nothing major wrong. good luck
16 years is a long time to be battling Yeast infections. Perhaps these aren't Yeast infections but something else.
What all have you been prescribed for this?
Any other medical conditions, i.e. Diabetes? Taking oral contraceptives?
Are you bathing or douching with perfumed products? Using feminine products that are perfumed?
You are seeing GYNs....correct?
As the above poster suggested this could be something from your partner and he is reinfecting you over and over.