A persistent cough lasting 30 days that worsens at night and has not responded to amoxicillin, ambroxol, or dextromethorphan requires a professional medical evaluation. Since antibiotics did not help, the cause is likely non-bacterial. Common culprits for a night-worsening cough include cough-variant asthma, post-nasal drip, or acid reflux. I highly recommend consulting a physician or pulmonologist who may suggest a chest X-ray or lung function tests. Depending on the diagnosis, effective treatments could include inhaled bronchodilators, corticosteroid inhalers, or antihistamine nasal sprays. Do not worry; chronic coughs are very common and highly treatable once the underlying cause is correctly identified.