I know you can use saline drops in the nose to help clear the nasal passages (they sell them just for babies). I don't believe you can give anything else to one so young. Putting him in the bathroom with you while you shower helps clear his nose and loosen congestion in the chest. A humidifier in his bedroom can help alleviate the congestion as well.
Good luck getting him to sleep. Babies have a difficult time when they are forced to breath through their mouth. Plan on not having a great routine, his possibly skipping naps (or shortening them) because of discomfort and then sleeping at odd times because of exhaustion. I wouldn't worry about skipped naps as much as loosing nighttime sleep - a pattern you don't want to set. He's so young that you may consider doing what my pediatrician recommended, putting him to sleep in his carseat (in the house, not in the car). That way the fluid from his nose doesn't drain into his ears and you might avoid an ear infection.
He will get better soon and then things will return to normal. If you notice him feeding less because of his illness, try to pump so that you don't have a supply issue a week down the road when he starts feeding robustly again.
