Girls hi! Our little one is 7 months old and coughs really bad with ph…

Girls hi! Our little one is 7 months old and coughs really bad with phlegm up to the floor, I spray a physical solution and she breathes through a nebulizer, today we went to see a pediatrician, he says her lungs are clean but prescribed an antibiotic. Yesterday's temperature was 38, today it hasn't been. I don't want to give antibiotics... What should I do?