Hello. Thank you for asking at HCM. I went through your history and would like to make following suggestion to you: 1. Drugs like Xyzal (antihistamines) treat symptoms of the allergy, not the allergy itself. Hence as long as one has allergy symptoms, one has to take them repeatedly. 2. Common side effects of Xyzal (& similar drugs) are sedation, drowsiness, poor concentration, etc. If you are not experiencing such side effects, you can take it for long duration as it usually does not have long-term side effects. 3. Yes, allergic rhinitis and sinusitis are closely linked. So Xyzal can improve symptoms of sinusitis. 4. Were I treating you, I would also add montelukast in addition to Xyzal. 5. Personally I would suggest you allergy testing which will help you identify what you are allergic to and how to avoid them. 6. A balanced diet rich in vitamins & minerals (adequate amounts of green leafy vegetables, fruits, sprouts, etc) and avoidance of exposure to dusts, smokes & air pollution will also help you in a long run. Hope above suggestions will be helpful to you. Wish you the best of the health. Thank you & Regards.