It doesn't sound like a Mite probelm, due to the timing. As others have stated, mites need a host to be able to survive and breed. If the bedding has only been in the tank for 6 days, there is no way that any stray mite eggs in the bedding could have hatched and grown to that size in that time period. Nor do I think it is possible that that population of mites could have gotten into a bag of Aspen at a store. If you want to check your snake for mites, take a white paper towel, wrap it around the body, and starting from the tip of the nose, let the snake crawl completely through the paper towel. Open the paper towel and inspect for black dots that walk.

p.s. Wood mites will get on your snake, I see them on mine all the time, but they do not feed on them, and thus will not injure the snake. However, wood mites in large enough numbers can be an irritant to a snake, just like a bunch of bugs walking around on you would aggravate you.

Hope that helps,