Have you tried probiotics yet? Apple cider vinegar as well in his water. Massage crop without vomiting him.He is quite stressed from it so we've stopped, but he's not doing very well. As for the antibiotics, a vet suggested them to us after we took him to her. He has a bacterial case so she thought they may help.
I've also heard success stories with medication for yeast infections. Sour crop is a yeast infection.