Can you see any sign of parasites? Egg cases at the base of feather shafts, "dirt" under raised up leg scales, tiny dark freckles on the skin? If you know what parasite you have, it is much easier to get rid of.
What did you dust with? DE? Or a permethrin product? If you can figure out which parasite you have it will be easier to know how to kill it.
As for protein... my local store carries a 20% protein layer feed. However, any meat trimmings work well, also I think calf manna is high in protein and is usually there with the feed.