Brown/black armpits

Erin

So I’ve always had issues with having dark armpits ( but never this bad ) and I usually used a foot powder to help keep the darkness away. But here the past few weeks it’s came back and gotten so much worse and it burns and I’m in so much pain! I haven’t shaved or used deodorant in a few ways because it hurts to even touch them. I’m making a doctors appt tomorrow but does anyone have any advice or comments about what this could be?!