Welcome to BYC. Coccidiosis is usually seen after 3 weeks, but I would go ahead and finish the course. If the chick is lethargic, it may just need some water and food or be suffering from shipping stress. Can you check for any stuck poop on the vent? If you find any clean it off with warm soapy water and a tissue. It can recur daily for a week or so. Dip it’s beak into water several times an hour. If you have Poultry NutriDrench or or Poultry Cell, give 2-3 drops orally as a boost. Vitamins with electrolytes can be used instead in the water. If you cannot get any of those, mix a tsp of sugar and a tiny pinch of salt into a cup of water, at room temperature. Egg yolk and watery mushy chick feed are very good to offer.