u/3x12is36

I have these dots that appeared a few months ago and can’t find any images that look really similar. They are on the back of my knees mostly like the photo shown, but I also have one on my torso, one on my armpit, and I went to the dermatologist yesterday and she says I have a few on my back I wasn’t even aware of. They haven’t grown that I’m aware of, they are not raised, and they don’t hurt or itch. They’re just dots of discoloration. My dermatologist said she doesn’t know what it is and biopsied a couple. Does anyone have any ideas what could be causing them or what they are?