Why is my room so dusty?

[Freakbro]

windows open 24/7 is probably the answer.

I live near a road that's not even that busy most of the time and my window ledge inside gets covered in crap from cars etc polluting

Dust isn't just dead skin cells

This.

It's a myth that house dust is mainly skin cells, it's mostly made up of good old fashioned dirt particles, that will be coming in from outside.

The carpet will be another good source, as it will trap and store a lot of dust coming in.

To reduce the dust, don't have your windows open 24/7.