I started getting yeast infections about 20 years ago--nasty things that they are. I finally started watching what was going on when I would get one and figured out some very simple things to do which helped immensely. The worst times for me was during the heat of the summer, and after trying the following I rarely, if ever get one.

Wear loose, light-weight, cotton pants in the heat of the summer. Tight jeans will overheat you, which seems to result in the death of the bacteria that keeps this stuff at bay.
Don't ride in vehicles in hot weather with vinyl seats, either.
Avoid antibiotics unless it's a serious illness like strep throat or pneumonia.

About the only time I ever get one now is if I'm sick and run a pretty good fever. Otherwise, I've been infection-free for some years now.