I am so sorry! What a terrible thing to have happen!
I love my birds - don't get me wrong. But I am not sure I'm giving them a good life considering all the illnesses I've encountered this season. I MUST be doing something wrong. Maybe my run is not clean enough. But it's a huge run, and I'm not entirely sure how much cleaner I can make it. I spot clean, clean roosts and nest boxes daily. Fresh food and water every day. A thorough cleaning 1x or 2x a week. Good, fresh food. Limited treats. Regular health checks. Idk. I'll do my best by my beautiful birds, but I won't add any new birds.
You say "this season," like you haven't had anything wrong beforehand.
I'm going to be honest with you - last year I lost more birds and had them sick more than any other time I've had them in 5 years. This year I've had *awful* hatch rates in both my incubator AND broody hen situation.
Sometimes, bad years happen and then the next it's like nothing ever happened and your flock returns to normal. I've seen a lot of chicken keepers get sick birds more times than they can count in one year and the next everyone's fine.
Don't be hard on yourself.
Check food milling dates.
Check waterers.
And above all, remember that death and illness sometimes happens. Sometimes it's something we can't fix - you're not doing a bad job.