8 year old boy, average height/weight, low grade fever averaging 100.5 for around 4 days, chest congestion with productive coughing, no sore throat, sneezing on and off but not a major symptom, NOT stuffy, low appetite, low energy, he has vomitted a couple of times which I believe was brought about due to coughing, should I let this run its course or take him to a doctor?