Make sure you have the poult on Turkey Starter or Game Bird Feed. And, continue those vitamins.They require higher protein than chickens. I raise turkeys and quail and have mine on Game Bird Feed. You’re incredible to rescue that little one. I hope you are able to determine what’s happening. Focus on good nutrition and warmth. Hopefully, that will at least be enough to help the poult fight through it. I’ve never had one with a flabby-looking abdomen… only chubby, filled with the absorbed yolk after hatch. You mentioned that he was being trampled. An unwell poult getting trampled could’ve caused some type of injury in addition to already feeling unwell. I wish I could help you more and hope that he gets better soon!