What is this Dark discolored & dry-skin lesion on my spine?

[Thumby2020]

This area of my lower back is turning dark brown & growing bigger. I was getting dizzy, tired, thirsty, need to pee at night. I  thought with all symptoms it could be a sign of pre-diabetes, however all blood tests are normal. The skin looks injured (fading in & out for 2 months) & recently raised markings appeared — almost like a scar.  It doesn’t hurt or itch.  I’m 40 years old, very skinny, w/ polystic syndrome, very heavy periods whole life, sensitive stomach. I was wondering if anyone has seen something like this? Posting images