I have pcos and experienced this as well. After lots of blood work over many years we discovered that I had elevated prolactin, imbalanced cortisol, elevated TSH (thyroid), and a pre-diabetic A1C. I recommend having these test done if you haven’t already to see if any of these are contributing to your symptoms. Especially a complete thyroid panel as your symtpoms of fatigue and brittle nails and hair are symptoms of hypothyroidism.
Also, if you get your thyroid panel done make sure you do it in the morning as I was misdiagnosed for years because the TSH is highest in the morning and lowers as the day goes on so in my case because my TSH was only slightly elevated by the afternoon when I was getting it drawn it had fallen within a high end of normal whereas when we draw it in the morning it is clearly clinically hypothyroid. I have read that this is one of the most common reasons women who have hypoT are missed so just make sure you have your blood drawn in the morning.