There are a large number of anti-histamines (anti-allergy medicines) apart from cetirizine such as fexofenadine, hydroxyzine, clemastine, loratadine, mizolastine, embramine, promethzine etc. If an anti-allergic agent is required on a long term basis, it would be better to change the molecule from time to time so that adverse effects do not have a cumulative effect. Otherwise, cetirizine is relatively a safe agent. Its side effects include: drowsiness, headache, dry mouth, dizziness, agitation, GI upset, aggressive reaction, convulsions, somnolence, fatigue, and pharyngitis. Cetirizine does have rebound problem when discontinued abruptly. In view of your persistent problem it might be better to determine the exact allergen(s) and then go in for desensitisation to root out the disorder at a good allergy clinic.