Julie depending on your vet or location in WV you can contact UK and they will send you what you kneed for Necropsy. I have done this with some chickens and they were very helpful. Turned out in their cases it was brain trauma silly silkies bumped their heads. Sorry for your loss and I wean Billie's at 2 months because they can mate at that point. Does I will leave on moma earlier but if they are eating grain I pull off the bottle I will use the calfmana milk pellets mixed in from TSC. I know everyone has opinions on this its just what has worked for me. My friend had a grown Nubian fall over dead when the temp changed like it did. She had just got the goat 3 days before. I think combination moving and change in weather. How long had the little one ben outside? If it was the one in the house then was only out a few days when it was nice then got cold its coat may not have been warm enough if it didn't have enough straw or other goats to cuddle with. I moved my babies outside on the warm day and I have 2 heat barrels out with them. They are also in with the young chickens normally I would not do this but I am out of room. Again sorry for your loss.
So very sorry, i know what its like to loose a baby you put so much energy into.
It would also have been silent pneumonia. I lost one earlier this year, he was fine in the morning, and he died that night in my arms. Its a swift killer.