I get a daily email from the author of "what to expect while expecting" and I just got this one a few days ago...It offers a few things that can safely help.
Week 16: your nose always knows: nasal stuffiness
your uterus is not the only thing that's starting to swell. The mucous membranes of your nose may also start to swell from all the pregnancy hormones circulating in your body, which are also increasing blood flow there. The result? Your nose probably already knows: congestion, and possibly even nosebleeds. Unfortunately, the stuffiness may only get worse as your pregnancy progresses, but your practitioner will probably not prescribe any medications or antihistamine nasal sprays to help clear things up (but do ask if he or she recommends something else instead). You can safely try saline sprays or nasal strips, especially if the congestion takes a turn for the truly uncomfortable. A humidifier in your room and a little petroleum jelly dabbed under your nose may also help overcome the dryness associated with any congestion.