He's been weakened pretty badly through being injured and re-injured...you're going to have do some hard work and take him to the bin manually a LOT of times... You'll see a little change in the status bar after about 8 feedings... and just keep on going.. or give yourself a break, give him some water, let him farm a couple of minutes and then repeat the routine. He will get back health, but it's going to take sme work and patience on your part.

Oh and try making him a doctor... let him get a notch of experience ... you'll find doctors tend to eat and drink on their own more readily