I'm copying some information I got from www.askdrsears.com, in the past when we've had congestion, I've done several of the mentioned natural remedies and they have worked. Hope this helps and he is feeling better soon!
M.
NATURAL TREATMENTS FOR COUGHS, RUNNY NOSE, AND CONGESTION
Steam cleaning. Give your child steam, steam, and more steam. For infants and young children, turn the bathroom into a steam room with the door closed and the shower on full hot. Sit in there for 10 or 15 minutes. For older children, use a facial steamer or pot of hot water (carefully!). The steam will help loosen the nose and chest congestion, and help your child cough it up or blow it out. Do this steam cleaning every morning and before bed, as well as during the day if possible.
Clap the chest and back. While you sit in the bathroom steaming, clap on your child's chest and back (where the lungs are) firmly (harder than burping) with an open hand. This helps shake the mucus loose so your child can cough it up better.
Sleep upright. If possible, allow your child to sleep in a slightly upright position. This allows for easier breathing during sleep.
Nose hose. For older children, it is crucial to have them blow their nose several times during a steam cleaning, as well as frequently throughout the day. Getting out all the junk will help prevent this from turning into a bacterial infection. An alternative to steaming is to use nasal decongestant spray to loosen up the nasal congestion before blowing it out. For infants too young to blow their nose, you can suction them out using a blue rubber bulb syringe.
Hot steam vaporizer. Use a hot steam vaporizer in the bedroom at night (not a cool mist humidifier). This warm, humid environment can help keep noses and chests clear at night. Be sure to air the room out well during the day because mold can start to grow in the room due to the warmth and humidity.
Dr. Sears suggests: To prevent burns keep your hot mist vaporizer out of reach of infants.
Eucalyptus and lavender oil. Add only one drop of each of these to a facial steamer, pot of hot water or some vaporizers. They can help clear up the congestion faster.
Vapor rubs on the chest. Occasionally, these can cause wheezing because the vapors may be too strong for some children, but overall they will work well. It is safe to try, but do observe your child to make sure it doesn't cause wheezing.
Drink twice as much liquid. This will help to thin secretions and prevent dehydration.