Oh, N.! I feel for you. My 4 month old has already had two colds this season--I think we've been passing it back and forth. Here's what I did:
-let him sleep sitting upright, in a bouncy seat or a swing, so it's easier to breathe.
-Use a cool-mist humidifier, or a vaporizer. You might try the vicks plug-ins, but sometimes they irritate more than help. Whatever you do, don't use the vicks vapo-rub, even the baby kind. It irritates their skin and doesn't help more than the whole-room kind.
-If you don't want to get a vaporizer or humidifier, take him in the bathroom, shut the door, and run the hot water in the shower until the bathroom gets steamy. That should help loosen his congestion so it'll sneeze out. (You could also try the sucky thing, but I never do--I'm not good at it, my son hates it, and our doctor says it's not effective enough to make it worth annoying the babies as much as it does. :-))
-Encourage lots of sleep, and don't go out a lot. Even low-key stuff can be exhausting, and makes colds linger.
Our first cold lasted 3-4 days, and we're on day 3 with the second one (which now includes an eye infection...*sigh*) but they DO pass. Good luck!
(And yes, it IS hard dealing with a sick baby when you're also trying to work. But you do your best, and everything turns out okay. I'm back at work now (I'm an attorney) and while our being sick has made things more difficult, I've found that we can soldier through. So can you!!!)