I suggest not using NHS direct, you will not get any sensible replies!
Option 1. Use Otrivine 30 mins before take-off. Quick fix, will work in many cases, however long term use will your nasal septum to erode. Not a permanent solution
Option 2. Work out what is actually wrong. Do you get hayfever/ allergy symptoms? Are your symptoms seasonal? Are you allergic to house dust/ pets etc? If so steroid sprays are likely to help. Modern sprays can give relief within 3 days, and some can be bought over the counter (eg Flixonase).
Option 3. Do it properly. See a GP, take their advice, and if things don't settle ask to be referred to an ENT surgeon. Before being considered for surgery decongestants and steroids will be tried, and a CT will be performed to check that your problems can be helped with surgery (not all can). The surgery involved is called FESS (functional endoscopic sinus surgery) - like all surgery it isn't without risk, the frontal sinuses are a tad close to the brain & the eyeballs! It has sorted out many professional pilots though.
Be careful taking decongestant tablets if flying, many are sedating & have been documented to cause CFIT.......
The pressure changes that develop in the ear in flying are not usually enough to cause permanent damage (unlike diving), but will disable & you certainly shouldn't be in control of a plane if you can't equalise or are getting distracting sinus pain.