Colds/flu

My 4 year old has this cough and has had for about a month n a bit, everytime it seems to be getting better he goes back to nursery n after a few days the coughs back again iv been giving him medicine,honey lemon hot drink, trying my best to keep him cosy n warm and been to doctors to just be turned away again saying its the cold am honestly running out of things to do for him n it's breaking my heart to see it keeping him awake n hurting his wee throat, any tips and tricks on helping him would be greatly appreciated