I feel your pain!!
I was getting between 12-15 eggs a day up until 3 weeks ago. Now it's steadily declining and is at 6 eggs per day
I have sent a fecal away and will treat for worms and lice next week.
I have added vitamins to their water.... HOpefully things will improve soon.
Just wanted to let you know you are not alone.
I was told by various people that it is normal - that they cycle like that.
Are they showing any other symptoms, coughs sniffles?
Is there something that could be stressing them?
You may want to send a fecal sample out to make sure you have gotten all potential worms.
You could add extra protein and some greens to their diet - kind of hard with 100 hens I guess.
Do you have poultry extension service in your state/province. Someone you could perhaps call and ask for input.
I'll be calling our Provincial poultry veterinarian specialist this week to ask for input - I'll let you know what I find out.
Anyhoo, I hope it gets better soon