My hamster seems to be scratching a lot? What's going on?

I notice my hamster seem to scratch itself all the time but the thing is I spray the mite and lice thing on her almost once a week and there seems to be no signs of mite or lice or fleas???I use Aspen bedding and feed it nuts and others...all suitable for her. Can putting to much bedding cause this?? I also bought it chinchilla sand.