Okacet (cetirizine) is generally safe for long-term use, but taking it every three days only provides temporary relief without controlling the underlying inflammation. Your symptoms, which worsen with summer heat and scratching, could indicate cholinergic urticaria or a heat-related allergy. To treat this effectively, taking a daily non-drowsy antihistamine (like Cetirizine, Fexofenadine, or Bilastine) is usually recommended for continuous control rather than sporadic dosing. Please consult a dermatologist for an accurate diagnosis and a personalized treatment plan. Meanwhile, keep your skin cool, wear loose cotton clothes, avoid scratching, and apply calamine lotion for soothing relief.