I'm a teenager coughing for over a month now with green phlegm and also finished a bottle of cough syrup but to no avail?

Coughing: you need to see the doctor about the possibility of sinus infection to get treated for it

Consult your Doctor: You have had cough with green phlegm for over a month You should consult you Doctor for diagnosis and treatment.You may need antibiotics after diagnosis is established

Workup/mgt: If you have been coughing for more than 4 weeks with green phlegm, you may have a bacterial infection of the upper or lower respiratory tract. Please obtain an appointment, a chest radiograph may be performed. Pulmonary consultations available on my virtual practice, and imaging studies can be uploaded. In addition, if you can a sputum culture should be sent to determine the underlying cause.