You should consult an ENT specialist. Teeth and sinus are close by structures and symptoms overlap many times. A CT scan of the sinus and a culture test would be able to diagnose the issue. Following would be the treatment protocol (some of which you are already doing);
1) Nasal steroid; decrease inflammation and open up obstruction.
2) Oral decongestants such as pseudoephedrine are often helpful.
3) Topical decongestant for short duration.
5) Steam vaporizer
6) Eucalyptus oil may help
7) Nasal saline irrigation
8) Vitamin C
9) Antibiotics; only if nasal culture is positive and there are signs in CT scan.
For treating it naturally; steam inhalation, nasal saline water (salt water) irrigation (can be done by Neti-pot), Vitamin C, Eucalyptus oil inhalation can be done. Following can increase the body immunity so help in overcoming the sinus infection;
1) Omega 3; Fish oil capsule and flaxseed oil capsule.
2) Ginkgo Biloba
3) Zinc 30 mg.
Please feel free for your follow up questions.