I'd try treating for sour crop/yeast/fungal infection if there's still liquid in the crop in the morning.
Does he normally roost at night? That may be helpful.
Can you get video of him? Upload video to Youtube and provide a link.
Where are you located in the world?
What antibiotic are you giving and the dosage?
Was a fecal float done to see if worms and/or Coccidiosis are part of the problem?
What's his poop like?
How old is he?
What do you...