This could be an RSV infection
. Keep in mind, RSV is typically not as severe in the second year of life as it is in the first. However, your son's worsening symptoms, combined with his young age, is a good reason to have your doctor examine him again. It is most likely the same harmless virus (RSV or otherwise), but in babies it's always best to be certain. No pediatrician
would fault you for getting a second look.