Netti Pot's are great (although very disgusting really!) They really work and they are totally safe for breastfeeding if you are doing that. I also used some Vicks sinus spray once when I had a really bad sinus infection when DS was about 4 months old.
My Dr will give antibiotics for sinus infections if you've had the stuffy/runny nose for 5+ days. Any less than that they usually tell you to come back (so when your dr asks how long. . .wink wink).