You are experiencing die-off. Die-off is when the body is detoxing and the initial symptoms get worse for a while.
The body gets used to dealing with parasites and toxins in certain ways - some get headaches and body aches, while others will have rashes and dry hair, while still others will have allergy and sinus problems. While detoxing - these will get worse because the body has already established a "route" in which it chooses to remove toxins. In your case - it is the sinuses.
Try to stick with it if you can - it will get better soon.