its mostly likely because the sunglasses aren't fitting correctly on your face. I bought $450 Carbon Fiber Oakley's and they fit so well but that was after I went through like 4 different kinds of fitment.
Mineral glass is a lot heavier than plastic. (and plastic attracts dirt because it's more electro static than mineral glass)
Try to get them fitted by a professional optician. Buy them there unbranded, rather than branded online or in a accessory shop or at Walmart. Or you can try adding silicone or rubber nose pads on them.
I think it's normal, even tho I don't wear sunglasses, I do wear regular glasses and the nose pads use to always leave a mark, they don't leave marks any more since I put little foam pads over my glasses plastic nose pads.
They do, but only if I wear them for a really long time. I think that the heavier sunglasses tend to be the ones to leave the biggest marks. Try to find a pair that's lighter in weight. My sunglasses were like 10 euros from h&m, and they're super lightweight.
It must be tight or you been wearing them for too long. I usually get marks when I wear my coolers more than a couple of hours. I haven't found one that fits me perfectly they either too loose or tight since I got a small face.