chicken pests

I currently have 3 adult hens and a few months ago I discovered that there were fleas or lice or other small parasites around their vent area. I had the chickens checked out by a vet, who gave me ivermectin to treat them for 6 weeks. I also dust them and their coop with DE quite regularly. But...

Found mites on two of my chickens (both Sussex breeds) ear lobes and waddles. How would I go about curing it? If I have to buy a product to clean it what should I buy?

I have a room with concrete floors and wooded walls and a door. It is out in a covered indoor shop. I had deep cleaned the shop for preparing my breeding season ( hatching chicks and raising them) I keep the place very clean and tidy. Yesterday I went in the room and I noticed maggots underneath...