My Son Has Had A Bad Cough For About 10

my son has had a bad cough for about 10 days and 3 days ago he broke out in a rash. the rash is on his whole chest, abs and armpits. it is not bright red or swollen looking. it is just a ton of light red colored bumps. his cough is still bad and keeps him up al night. his nose is runny with green snot but there is only a mild temp reaching 38.2