Feeding layer every other day isn't going to give you good production. They are probably not getting enough protein, I would switch to a higher protein feed like an all flock and let them eat as much as they want. Provide a separate dish of oyster shells for the extra calcium.
You didn't mention how old they are, some are quitting now to molt. EE aren't always good at production, for me they have been hit and miss.
I'm sorry, I thought the egg shells were enough calcium for them? That's what I had read when I researched it. Didn't feel like I need to spend extra on oyster shell when they already produce calcium. But I can give it a try. We will also start feeding them every day to see if that helps. They are a year old this month.