Sinus pain can be due to a number of things. If you are classically atopic or have a propensity toward atopy, then it may be that nasal polyps are the root cause. One of the problems with polyps is they often invade into spaces high up in the nasal passages (ethmoidal sinuses) that are hard to get to with regular sprays. However, Fluticasone Propionate (Flixonase) can be obtained in a capsular form that you can get to the right region. You do have to kind of bend your head backwards while lying down (like over the back of a bed) and this is a bit of a pain twice a day, but they do shrink polypi.
Alternatively, you could get a CT scan to assess the extent and a polypectomy. Maybe see an ENT surgeon...
P.s. I don't work for GSK!!
Happy pressue equalisations