Sinus congestion, cough, and some of the other symptoms your son is suffering from can all be caused by the same types of bacterial or viral infections. Typically, an upper respiratory tract infection will begin with minor symptoms, such as cough and runny nose, and then either clear up (most of the time) or progress to more stubborn and persistent symptoms, such as sinus congestion or deep cough.
The best rule of thumb is that whenever the symptoms have not gone away after a few days or are getting worse (as they sound like they are in your son's case), then you should go to see a doctor
. Your son's pediatrician
will be able to perform a full examination and help figure out whether any additional treatment is needed.
The types of things that will need to be ruled out would include a true sinus infection or a serious lung infection such as pneumonia. These can both be triggered by an initial common cold or other similar infection, and they usually need to be treated with prescription antibiotics.
If on the other hand your pediatrician determines that this is just bronchitis
, then antibiotics will most likely not be necessary, although medications to help relieve the cough and other symptoms may be of some use. Again, please discuss this with your pediatrician soon.