The tricky thing about dealing with sinus issues is figuring out whether they're pregnancy-related. That's because pregnancy can cause the blood vessels and membranes in your nose to swell, and it can be tough to breathe through your nose — even if you're not sick at all. If your symptoms are just pregnancy-related, saline nose drops and running a humidifier at home can help you feel more comfortable. If you're sick with a sinus infection, those treatments can help, too, but you'll probably have to wait it out. Luckily, most sinus infections do go away with time. The exception is a bacterial infection, which will likely be accompanied by fever and possibly yellow or green mucus; for that, your doctor may prescribe a pregnancy-safe antibiotic.
Before you take any medicine, check with your doctor. Things like Sudafed and Actifed are fine for most pregnant women to take for a short period of time, but pregnant women with certain medical conditions, like hypertension, should avoid them.