Not getting your period, pcos, and insulin resistance are are candida symptoms. It’s my belief that if you cure your candida you will get your period back naturally.
I’m not familiar with metformin, but it sounds like it’s working on your endocrine system? Maybe adding extra hormones?
Is “not getting your period” your only symptom if you stop taking it? If so, then it seems to me that the metformin is just a band aid for your candida symptoms.