For heaven's sake! Start with the simple stuff! Ask your GP to do your IgE levels especially for dustmite and other allergies. Having had problems with stuffed-up sinuses for several years I came to the conclusion that it might just be an allergic reaction to something so went and had a chat with my GP. The IgE levels came back at more than 6 times the upper limit of normal for dustmite. I now take an approved (by the CAA) antihistamine and very rarely have any problems even though the last IgE level was approximately x12 the upper limit of normal.