Recurring vaginal yeast infection

I’m 26 and unmarried. I’ve been repeatedly getting a vaginal yeast infection for almost six months now. As soon as I get it, I start with the treatment and then it seems to go away but then when my partner and I have sex, it resurfaces. I’ve had multiple tests done and have been given the same medication pretty much - both oral and vaginal. I also don’t use scented soaps or any such thing. Instead I use Keta-Zole+ to wash myself. And I take extremely good care of my hygiene.
But in spite of the all this it’s just repeatedly happening. I don’t know what to do anymore. Please help.

What type of underwear do you use? Stick to cotton only.

My doctor had previously advised to try to not wear any if possible. And since I’m at home most of the time due to the pandemic, I usually don’t wear any. And even when I do I wear cotton. It’s still recurring every month.