Don't think Poultry Protector will kill an infestation of lice or mites.
Are you sure the bugs are gone?
Best to get some Permethrin.
...and.....
Part the feathers right down to the skin around vent, head/neck and under wings.
Best done well after dark with a strong flashlight/headlight...
There could be a plethora of problems.
Tell us about your coop and run, with dimensions and pics.
What all and how exactly are you feeding?
How old are your birds and how long have you had them?