You said he was a broiler chicken, and they are usually butchered at a young age, around 6 to 8 weeks old here. How long are you keeping him before you butcher him? It is difficult to know what exactly is wrong with him, but the white poop is usually from dehydration, while the green is from not eating enough. If you give him antibiotics, you probably will not want to eat the meat. Usually sick chickens will eat chicken feed mixed with a lot of water. Cooked egg, tuna, and liver are also good. What are you using for chicken feed?