Persistent cold symptoms without nasal blockage for three months often suggest allergic rhinitis, non-allergic (vasomotor) rhinitis, or post-nasal drip, which can sometimes be triggered by acid reflux (GERD). If your main symptom is a lingering cough, it could also indicate cough-variant asthma. While over-the-counter antihistamines might offer temporary relief if allergies are the culprit, a three-month duration requires medical evaluation. I strongly recommend seeing an ENT specialist or an allergist. They may perform allergy testing or a nasal endoscopy to pinpoint the exact cause and prescribe targeted treatments.