Lurker here... I had to answer as I feel your pain. I had this problem at the begining of the pregnancy - I am now 21 weeks and it is under control.
I have had skin issues for almost 6 years. While I was nursing my baby 6 years ago I started breaking out in a red raw skin on my nursing area. THen all over my chest. I eventually stopped nursing my baby because it hurt and itched so bad. I thought it was thrush and treated it as such over and over again. It only got worse. I tried diet, herbs, nystatin, everything for YEARS. It never really went away although it did eventually go away from my chest only to show up "down under - perineum area mostly, and behind my knees then between my eyes! I tried eveything all over again. You name it, it tried it. Tea tree burned it (I am an Aromatherapoist and know you should never use tea tree undiluted down there) but it was worth the try. Everything seemed to make it worse. Drying things like baking soda worsened it, oils like coconut oil worsened it. It was so bad I was missing sleep - for a few years...
Then I stared looking at other possibilities - Turns out it is eczema and psoriasis. Putting anything yeast related on it made it worse which made it flair up worse and made it last longer. I started taking flaxseed oil and putting diluted (half water/half organic apple cider vigegar on it. Slowly, it started to go away. I put it on wherever i have the itchies and i use it after I "wipe". I use diluted ACV on a cotton ball and leave it alone. I do this daily and after 6 YEARS of issues, I am not itching anymore. I only started doing this about 10 weeks ago, and i am finally comfortable.
Anyway, do not use tea tree oil undiluted on you privates. You can put it directly on a tampon and that works for true yeast and BV, but it will burn putting it in. For the outer ares, you can mix a few drops of tea tree with a tbsp of olive oil and that will still do the job - if it is yeast or bacteria - and it wont burn your tissues. I however recommend ACV, as it too will help if it is yeast, but if it is more of a skin issue it will help that as well. And it wont burn your tissues. It will sting for a minute if you are really raw, but that should stop shortly. It will probably take a few days to get better but it is a cheap, easy cure that worked great for me and is OK for pregnancy.
That is my experience and advise if you want it