You could try giving him electrolyte solution. (Sugar water with a little salt in it, either homemade or Gatorade or Pedialyte.) That would at least get some calories in him and buy you some time. With more strength he might feel like trying to eat again.
My local feed store carries 2 types of Save-A-Chick brand powders to mix in with water. One is called Electrolyte and has added vitamins in it. The other is called Probiotic and can be used with the electrolyte solution. They are in dark blue 3 pack pouch strips like yeast comes in. Pet stores might also have them.
Moistened food or yogurt might also be more appealing. I'd offer it all.
These guys eat and drink as often as they sleep so offer food and drink very, very, very frequently.
Good luck with your baby.