Help needed !
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Did the vet give an indication of why he was ill?
Is he getting pecked on - the reason for the bleeding comb?
Wash it off, apply some bluekote, plain neosporin or vetericyn spray to the comb, they generally heal quickly.
For mites/lice Clean the coop and bedding, give him a good dusting with poultry dust or try one of the treatment/suggestions in the following links:
Is he wasting?
It's possible he's has an illness such as Marek's.
Ivergen(Ivomec) can be used for mites, but you still need to provide bathing area(s) and follow preventive measures to keep them under control. Treating your coop and changing the bedding will be helpful in eliminating some of the sources/cracks where they can hide.
Also if you have not wormed him you may want to talk to your vet about treatment of those as well - they can cause weakness, weight loss, etc.
Try to restore his weight by feeding a poultry ration of at least 18-20% protein, scrambled/hard boiled egg, tuna, salmon or meat. Limit treats to no more than 10% of his diet, use some fresh greens, fruits, veggies, meal worms or sunflower seeds as treats instead of corn. You may also want to add vitamins or probiotics to his water to see if that will help.