I took metformin extended release for over 6mos for insulin resistance a few years ago. I lost weight, and was doing well, overall. But the diarrhea came back with time, and then I developed a severe vertigo (neuropathy in my ear), which one doctor said was due to the metformin, so I had to stop it.
I just couldn't function with the severe dizziness, etc. I could barely walk.

Metformin is a tough drug, IMO...to tolerate. Some people do well on it, others like me, just bomb out on it.

But if symptoms reappear later, that would be a sign that metformin should be changed.

There is a supplement called d-chiro inositol which will improve fertility too. It is OTC and not covered by insurance. I am taking that now, instead. It does cost alot of money.... I see it has come down in price to $59/month. When I started it, it was $85 per month!
https://www.chiralbalance.com/store/index

I do not recommend the other company online who makes this. They are slow in response, up to 3 weeks to get it, etc. Not as forthcoming for questions etc.
One thing the Chiral Balance is great for, is the facial hair that PCOS can cause. Mine is 90% gone now with this supplement.