Where would you say the congestion is? Throat, chest, nose?
Is he coughing?
Is there any discharge? If so what color?
Is he eating and drinking?
Theresa
For the most case if this is a virus then you need to let this run its course. Some things you can do is give the benedryl you picked up at 1mg per pound twice daily. You can also take him into the bathroom and run the shower to create a steam room to help loosen and mucus in his nose and throat. You can also pick up lil noses decongestant drops from your local drug store. This must be given on a tapered schedule to prevent rebound.
Days 1-3: One drop in each nostril 3 times daily
Days 4-6: One drop in each nostril 2 times daily.
Days 7-9: One drop in each nostril daily.
Days 10-13: One drop in each nostril every other day.
With his age there are other possible causes including poor dental health. In this case he could have a serious tooth root infection that has penetrated the sinuses. His constant swallowing of bacteria can also cause throat irritation.
Also, with age comes possible heart disease and lung issues. If the cough doesn't resolve or continues to sound fluidy it would be a good idea to have his chest listened to and possibly an xray to rule out heart disease and fluid on the lungs.
Please let me know if further assistance is needed.
A Voice for Your Pet
15 years experience in small animal medicine