You could send them to the State lab at VA State, but I don't really think you need to at this point. It is amazing with all the chickens around that so many survive.
If you were starting to see more than one have this problem, then by all means, send one it. However, just one is not cause for going that far.
I am sorry you lost him. With all the birds I have had around here the last 3 years, I still get an sick feeling when one dies or I have to put one down. The younger they are, the harder it is.
As for the poop, there is actually a poop page on here somewhere. Chickens can have a wide variety of the appearance of their feces and still have it considered normal. Seeing a bloody mucous once in a while isn't uncommon, but it you actually are seeing blood and a lot of it coming out, then that can be cause for alarm.
I think it it were a sour crop issue, being that he was so young would explain why he didn't last longer. They are growing so much and need those nutrients that are suddenly shut off. It is hard to see who much weight they lose too because their feathers are fluffy enough to hide it. (I just wish I had fluff to hide my fluff
)
Bury him in the garden where he can make beautiful things grow and go back to taking care of the survivors.
Sometimes you got to take the bad with the good.
Hey, your Pink Chick is still with ya, right?
Good luck and may all the rest of your flock be happy and healthy. From what I have come to know of you through your posts, you will properly spoil the heck out of them!