It is possible that when you bought the snake that it already had mites and it was just not a bad case. Obviously, they will continue to breed and become more noticeable when there are more of them.
However, yes, it is possible that the mites may have come from any new bedding you got.
I would suggest throwing out all of the bedding and use paper towels for the time being, clean any artificial plants/trees/logs with a half water half bleach mix and rinse well with water. If you have any real wood decorations, I would also suggest throwing them out rather than trying to treat them, but if you don't want to do that you can try baking them in the oven. Also, wipe down the cage with the half bleach and water mix to kill any eggs/mites left behind. Then when you get the P.A.M. treat the new bedding and you should be good to go.