I get sinusitis all time time, the pain in my face is so bad I can't even concentrate (happens more in winter than summer).
I would advise you to get tested for allergies if you can and also ask them to check for polyps in the nose, it's not a pleasant experience but good to check anyway. As for medication, I am on a steroid nasal spray permanently but steroid nose drops worked much better for me (but I can't get them at the moment because there's a problem with the supply here, worse luck).
If it's really bad they put my on antibiotics, 500mg three times a day for a week which sometimes works, sometimes doesn't.. really depends.
I would also suggest inhaling menthol crystals. If you can get any, just inhaling steam may help out. The other alternative which is really, REALLY unpleasant but desperate times call for desperate measures, is to inhale a bit of warm salt water. Only a little though. I accidentally inhaled quite a bit and was blowing my nose for hours!
If you manage to get rid of it for a week, I would really, really recommend you try and get a flu jab. I had to pay for mine but my Grandad recommended it to me as he has had the same sinus pain for decades and once he started having flu jabs, every year it seems to improve. Considering our ages, if we started now, we may be able to get rid of it entirely! This is my first year with it and I've already avoided flu going round that would have played havoc with my sinuses.
Hope some of this helps. It's an awful thing, I hate it but the doctors seem to know very little about it to help :(