Tried to hatch eggs 3 times from my flock but nothing fertile - what am I doing wrong?

[plum14]

Just an update I am horrified that we have a mite infestation on all the chickens .

So last night we cut away as many of the lice egg feathers as we could and treated with ivermectin and DE. Today I have scrubbed out the eglu.

But I'm hoping we get over this and it's the cause of the infertile eggs?

I'd had no reduction in egg laying and everyone seemed happy and healthy I feel rather guilty and neglectful.