Ways to prevent vaginal issues?

Are there any vitamins out there that help protect or prevent yeast infections/UTIS?? Being pregnant makes me have these frequently and I would like to know what I can do to help protect myself better. I drink plenty of water, am obsessed with yogurt, and all I wear are loose pants. I don't know what I'm doing wrong. Most of my underwear is cotton as wear. I just always feel red or irritated down there. (Been cleared of all stds) my doctor told me to not Google anything because it will always make you worry which is totally true, but didn't give me any advice or how I can prevent besides drinking water, yogurt, and cotton panties! Ughh!!