Narrowing down chickens

[Ballroomchick]

I have found a total of 4 shellless eggs in the run over the last week, none that I can tell have been laid in the coop and some days I get my typical 4 eggs and other days I get 1 or none. They are free range, I leave out a bowl of oyster shells and they have access to layer pellets all day.
I have a mixed flock of 6 hens that are all roughly 7 months old give or take a week. We just had our first snow and I know egg production slows when the temperatures drop.
Could it just be the weather is a shock to their system since they are still developing? How do I narrow down which hen it is?
How can I rule out diseases, malnutrition etc?

Help Please!

 

[BantamFan4Life]

How old is the hen laying shell-less eggs? Sometimes chickens will lay them when they just begin to lay.

 

[Ballroomchick]

Thats what I'm not sure. I bought them all at the same time in May and my guess is they were almost a week old, except one that has been noticeably behind the others in size and feather development by at least a week.
My two Red Sex links were the first to start laying back in August and have been consistent with good strong shells. My two Buff Orppingtons I'm nor positive which or if either of them are laying at all. One of my BO is the one that I think was younger than the rest, she's always been the runt and was the last to grow in her feathers.
My Black Sex Link I'm also not sure if she has layed yet or not. Same with my Rhode Island Red, I am pretty sure she is laying just because once when going to gather the eggs she was sitting on a couple but that;s the same spot one of my RSL likes to lay.

In other words I don't even know which chickens are acutally producing or how to figure that out.

 

[Egghead_Jr]

Hold them in the run for a few days to week, don't let them free range. The weather is far from so cold to slow down their laying so there is a good chance they simply are laying somewhere else. This will also keep them together so birds can watch one another and learn to use the nesting box. They'll stop laying in the run and you'll get a better idea who is laying by listening for the egg song and checking who is going to nest to lay and you can randomly just check the nest for a morning to see who is in there, color and shape of egg they lay etc. In a weekends time of paying attention you'll learn a lot.

 

[Ballroomchick]

Hold them in the run for a few days to week, don't let them free range. The weather is far from so cold to slow down their laying so there is a good chance they simply are laying somewhere else. This will also keep them together so birds can watch one another and learn to use the nesting box. They'll stop laying in the run and you'll get a better idea who is laying by listening for the egg song and checking who is going to nest to lay and you can randomly just check the nest for a morning to see who is in there, color and shape of egg they lay etc. In a weekends time of paying attention you'll learn a lot.

Well it has only been 10 degrees up here in idaho so i figured it was the change from 40 degrees to 10.
What do you think if i found small blood spots in some droppings today?