Vomiting young barred rock

[TwistedSerpent]

I have a 3 month old barred rock cockeral who right now is very lethargic and 'vomiting' a yellowish liquid. He was acting fine yesterday, however didn't go into the coop last night unknown by me. It's been in the 30's here. I found him this morning by the rabbit cages very lethargic, picked him up and he started drooling. There are barred rock feathers all over too however I see no blood or injury to him. He drank a lot this morning but hasnt eaten much yet. His crop is very full of liquid which he will drool out when you put pressue on it. It smells slightly sour but not overpowering.

Any recommendations or thoughts as to what's going on and how I can help him?