My husband of 37 years gradually lost not only his sense of smell but also his sense of taste. Over our marriage he has dealt with chronic sinusitis. He tried allergy shots, antibiotics and sinus meds. He got temporary relief, but the symptoms always returned. All that changed two years ago when he went on an anti-candida diet.
There is a wealth of information on the internet about candida, which is basically a yeast infection. To "cure" it, you have to eliminate sugar (which feeds yeast) and dairy (which increases the production of mucus) from your diet. After changing his eating habits, both his senses of taste and smell returned. A helpful book recommended by a doctor is titled "Sinus Survival." It is not easy to change eating habits, but it has made a world of difference in his health. A sinus rinse such as SinuCleanse is also helpful to get rid of excess mucus.