Lethargic chick with eyes closed

[RRandMercy]

I have one Ameraucana chick approx 3 weeks old that is lethargic and has eyes closed. She eats very little and drinks sometimes. I have been giving her Duramycin-10 that they recommended at the feed store for the last 3 days but I see very little improvement. I have also been mixing some electrolytes in the water along with the antibiotic and washing her eyes with a solution of 1 tblspn of distilled water and 2 drops of organic acv every day. Can someone give me any suggestion on what else to do? I am new to raising chicks and can use all the help I can get. Should I separate the one that is sick?