Hello and welcome to HCM, Difficulty in breathing which is variable suggests an allergic process. Due to allergy the nasal mucosa swells up regularly and causes difficulty in breathing. When the swelling disappears the obstruction to breathing disappears. Claritin d is an anti histaminic drug which controls the response to allergy, however, the underlying cause should be treated. The agent to which you are allergic has to be sought out. If the symptoms appear during particular season, treatment with anti histaminics will help. If the symptoms are more severe, and occur frequently, you need to visit your doctor for prescription of other drugs. this allergic reaction can also occur due to exposure to pollen, animal dander, dust, mite, etc. Try to avoid these agents. Thanks and take care Dr Shailja P Wahal