Oh my goodness! I have PCOS as well! And I'm not on metformin right now,but my left niple gets very tender and my right nipple is fine.to me it feels like a rash on my left nipple. Maybe its just something to do with pcos?? Hmm. Well anyway me and you should keep in touch! Get to know eachother because I don't know anyone with pcos.so it will be nice to share stories!