You shouldn't feel bad tagging someone to see if they can offer suggestions.
There's really no specific way to tag others, but if you've been a member for a while, you will see who mainly posts in each forum. For example, I'm mainly in the ER section, but will venture out sometimes. Others may...
I'm sorry for your loss.
If you lose another, then sending the body for necropsy would give you some answers.
You can look up your state lab here https://www.metzerfarms.com/poultry-labs.html
Photos of your birds and housing may help and possibly we can make some suggestions if they are...