I would have suggested Meniere's disease as well however, if you have had this checked out and found to be negative, then we can move forward to other possible causes. You mentioned the headache, certain types of headaches (migraines) can cause dizziness. Also, electrolyte imbalances can cause dizziness. Sinus issues can also cause dizziness as you mentioned. For the sinus issues, a CT of the sinus might be helpful. The ENT Dr can order the scan and tell you if you have issues. If so, they can treat you accordingly.