Off WebMD- Normally, about 95% of vaginal flora are lactobacillus bacteria. (These types are unique to humans, different from the lactobacillus in yogurt.) These lactobacilli help keep the vaginal pH level low and prevent overgrowth of other types of organisms... The normal vaginal pH is 3.8 to 4.5. Bacterial vaginosis usually causes the vaginal pH to rise above 4.5.
Now for a refresher in 6th grade chemistry (from Wiki):
Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline.
The pH scale goes from 0 to 14. Normally, the vagina is more ACIDIC than it is when BV is present. The actual number value is higher, but the further from 7 (neutral), the more acidic. Hence the H202 (an acidic compound) douche theory.
Now let's talk about your sodium bicarbonate (baking soda) claims. (Wiki): Sodium bicarbonate can be added as a simple solution for raising the pH balance of water (increasing total alkalinity) where high levels of chlorine (2–5 ppm) are present as in swimming pools and aquariums.
Yes, increasing alkalinity. Raising the pH number, making things less acidic. It is a pH raiser. It lowers acidity. Which is just the correct way of saying what it seems you mean. When you say we need to lower the pH of the vagina to combat this problem, you're exactly right. Which means we need to INCREASE the acidity.
SO, maybe an acidic diet contributes to BV in some way. Maybe an acidic diet somehow makes one's vagina more alkaline. I believe this did work for you. But it did not work the way you said it did. The doctors may have no clue, but that doesn't mean the solution is found in ignorance of basic science. That's how people end up taking things like Miracle-Mineral-Supplement
(also suggested in this forum, universally accepted to be a chemical normally used as industrial bleaching agent that has caused at least one death according to it's Materials Safety Data Sheet)