If you're washing (maybe even just rinsing and blowing) the next day, you may not be giving the products (especially the pour ons) enough time to get soaked into the skin and do their thing. We like to pour them at the beginning of one of those cold snaps when we know we won't be messing with them for a couple of days. If you can't stand that, try just blowing them out good for two or three days. I really prefer to wait 3 days after they've been poured to wash.
I think sometimes this time of year they just want to scratch - dry skin, too much hair, boredom, who knows why. The only thing that'll completely stop it is keeping them inside a hot wire, and eliminating everything inside their pen they can scratch on (feeders, etc...).