Have you tried probiotics? Those are known to help restore our flora. I also wonder if it is not yeast but another fungal issue. When they swab, do they get yeast back? I have had great success with the one day Monostat ovule for yeast, I must say. Sorry it has been difficult for you to eradicate this. There is someone here that swears by a salt bath. ?? Can't recommend as I don't know much about it. One other question, do you track it? Some women do have reactions to the feminine hygiene products they use and in particular tampons. Again, sorry . . . must be frustrating!
How is your diet? If you consume a lot of sugar (even fruit and things of that nature)- try to cut that way back and see if that helps. So sorry you are dealing with this- it has to be miserable!