Chicken lice, shaking head and now eye infection.

[animalsrus]

We have had chickens for three years now but last year we have struggled with health issues. They started with chicken lice that I tried to get rid of with DE and had to resort to Carbaryl Powder which did the job. Then I noticed that the chickens where shaking their heads, I have looked for mites in their ears but see nothing, would putting a drop of oil in their ears help? Even the day old chicks that where kept in a separate but attacked coop with a wire gate separating them have it, these chicks are now 4 months old and are in the same coop with the other ladies. Then today I noticed one of the chickens has a swollen eye, it looks like an eye infection, her upper eye lid if very swollen and looks as thought it has come to a head with infection. I need to resolve all these health issues before we get our new layers in the spring, any help would be appreciated.