I have a cough that produces lots of flegm, and is constant throughout the day with tightness in my chest (despite lots of fluids, rest, steaming etc)?

Cough: Sounds like a lower respiratory infection of sorts? If this has been ongoing for days I would recommend getting seen and treated.

Possibly Bronchitis: Difficult to confirm without more history & an exam, but u may have acute bronchitis, a viral infection that inflames ur airway, which can cause the persistent cough and chest tightness u have. I recommend seeking medical attention for a lung exam and possibly other tests to confirm acute bronchitis, an asthma exacerbation, pneumonia or other cause, and get an rx for an inhaler or other treatment