Suggest Treatment For Chest Cold After Treated Pneumonia In Past

my son is 3 years old, and came down with a head cold wed, it moved immediately to his chest (he is a preemie-grad, and has had trouble with pneumonia and rsv in past) he is running a temp, and his respiratory rate is between 48-50. I just don't know if i should wait it out a little longer to see what the day brings or take him in. I hate feelling like i'm always there for the slightest things with him, but his history proves medical intervention always was the case. It just seems so quick that a lung issue would be evident, when he only started showing signs of a cold wednesday night.