Sinusitis can brew in the sinuses unnoticed for quite awhile. You may have already had the infection, and the oil pulling triggered the sinsuses to cleanse.
A saline rinse is a good idea. Many drugstores have a squeeze bottle system called NeilMed sinus rinse, that is easier to use than a Neti-pot IMO. Adding just a drop or 2 of grapefruit seed extract can help kill the infection.
But I also agree with Molly, sinusitis can sometimes cross the brain-blood barrier. If the infection doesn't show signs of clearing, you should see a doctor.