3 week old is sick

My LO is 3 weeks old and has been very stuffy with snot for 4 days now. Doctor saw him on the second day of this and said he's full of snot/congestion in his head and nothing can really be done about it at this time. Dr said to have him sleep in his carseat for the first night so it can drain out some. What else can I do? Now He eats but then just throws it up right after. Any suggestions? I'm so worried about him.