L. Crispatus, L. Iners, L. Jensenii, and L. Gasseri. These are the probiotics (good bacteria) that dominate vaginal flora naturally, specifically L. Crispatus. They can quite literally kill and defend against the bacteria (and yeast) that cause the infections mentioned. When I started having sex, I didn't know how I could be affected by my partner. Even without STIs, and being monogamous. I was getting all the imbalances almost immediately. Yeast BV uti, one right after the other. I did some research and found which bacteria does what. I looked for products that contained as many of the bacteria mentioned. I bought doctors recipe Womens probiotics at the time for $45. They are now $16. I took them once for two weeks straight. After the first few days I noticed a HUGE improvement. I did not have to take them again for a while. Over the course of a year whenever I felt an itch, or discomfort or a smell, I took one. It's been years. I haven't taken them for some time and I haven't had any of those problems since. They. blew. me. away. So in addition to practicing sex safe and good hygiene, these probiotics can save you, and continue to protect over time. https://en.m.wikipedia.org/wiki/Vaginal_flora

Wikipedia has a pretty awesome summary of everything scientific, and all their cited sources.

Also a note on using yogurt: using plain Greek yogurt has been shown in studies to be helpful, and also I think we can all agree it feels good, HOWEVER the bacteria in the yogurt are not the bacteria that vaginas need.