Hello all- not sure where to start. I am new to raising chickens (less than 6 months) and im about to give up . Started with three big white hens and a giant rooster that looked to be leghorns but were far too big and the only 8 eggs they ever layed were very light brown. I planned on raising meat birds to eat with these chickens because of their size. My second coop held game hens given to me by my neighbor initially then i obtained a gold colored bird not sure of breed or age and a black and white not sure of age that i believe was a Dominique. I then got three free RIR (two roosters one hen) from craigslist said to be quite young. All of a sudden it started with bubbly eyes on gold one and coughing, then game hens were hunkered over with eyes barely staying open all puffed up. Hens were dying almost daily. I treated them with duramycin and it SEEMED. To help but then the Dominique started doing the same falling over, puffed up, eyes squinty. And ended up dying. Death seemed to subside for a short while . In the meantime i had five ducks that i had put in with the white chickens and one of the ducks died unexpectedly. After all this i decided to start letting all birds out to stretch their legs and let ducks go back to pond but that same day i noticed the big white rooster laying in a strange way as if he could not get up, i nudged him with my foot and he struggled to get up and seemed very uneasy on his feet and i noticed his comb which was once bright red and very pronounced was now flopped over, dark , spotty and pathetic looking . immediately put all chickens together in same coop and treated all once more with duramycin to try to knock problem out all together. The next day i noticed one of the white hens vomiting everytime she tried to take a drink of water. She became lethargic and sat around with eyes closed and beek open drooled and finally died. Since this last death i have continued to treat with duranycin and all seem pretty healthy other than the big white rooster. He still has same symptoms. I have still gotten zero eggs other than the eight i got long ago from white hens. I have pigs, ducks and rabbits that have not been problematic at all other than the one duck. What am i doing wrong. I feel as though i should get rid of all the birds, disinfect and clean coop and in the summer pick up new birds that are good layers already from a reputable breeder or hatchery. These chickens were purchased from local flea market and free. Noway to know age or health condition