Why do I keep getting yeast infection

Every month for the past 3 months I got a yeast infection. Can’t get an appointment with the doctor until next week so I will just treat with Monistat this time around. But any idea why I keep getting them? I’m 23 and I have never had this issue. Same sex partner for 3 years. Tested regularly for STDS. I shower daily. Cotton panties.

I’m so sick of getting them. Help please lol