I have posted this before, I get sinus trouble most winters and one of the most helpful things I have found is sterimar nasal spray. It costs about 6 quid and NHS docs can't prescribe it bit it really helps to wash out sinusses. Its is made from filtered sterilised sea water, has no side effects, can be used as often as you want/need is a gentle antiseptic and is also very soothing if the sinus is sore.
Its a bit disgusting to use, you spray it up your nose and the.....debris either runs down your throat or is blown out of the nose, even when the sinus is clear its amazing and a bit horrid what comes out.
I am not affiliated to the makers in any way, don't have shares in the company, I just have found it works