Yes, it is safe. For diagnosis -nasal endoscopy & ct scan sinuses

Y to take cetrizine twice a day..u can use cetrizine safely for 3 or 4 months..after that depending on the symptoms u can use..rather use a combination medicine or new medicine which may improve u symptomatically..u can take tab bilastine 20mg at night time instead of cetrizine..u can even use a fluticasone nasal spray if needed..for diagnosing sinus problem get HRCT PNS and Diagnostic Nasal Endoscopy done..

CTPNS should be done if you are suspecting sinusitis. Taking levocetrizine twice is not recommended. For nasal blockage and allergy you can use topical nasal sprays.

Avoid exceeding the recommended daily dose as ingestion of higher than the recommended dose increases the risk for somnolence. 5mg once day at bedtime is the usually recommended dose for adults. For nose block you have to take nasal sprays (not otrivin)