e. Coli takes about a week to run its course, a bit longer is possible, but no way seven weeks.
30 days on antibiotics he's probably got a yeast infection/gleet. Any yellowish stinky stuff sticking to his butt? Regardless, I'd put him on probiotics. There's powders you can get for their water, like Hydro Hen is one, or Greek yogurt is good too. If you are buying any of this, also pick up some Poultry Cell vitamins. You can put that in his water every other day and alternate with the probiotics.
I'm not sure what that feed is you have for him but if it's meant for chickens, then I'd wet it and make it into a mash. He may like that better. If it's not chicken feed, an all-flock type feed would be good for him.
You're sure doing well by him though. Glad you are saving him!