What are the next steps if I get a dull chest pain on my left side after walking for 20 minutes?

Well done indeed! Stopping smoking is the best gift you have given yourself and your family this New Year! You probably feel a better sense of smell and taste. By now more oxygen is reaching your heart and muscles easily and your immune function and circulation are getting better. However it will still be a while before risk of heart disease drops significantly (up to 2 to 5 years) and will take longer (up to 10 to 15 years) to approach that of a non-smoker.

Hi, you should definitely see a doctor/go to A&E immediately as a matter of urgency, as your chest pain has lasted for weeks and has shown signs of worsening. Chest pain is one of those symptoms that you should NOT ignore. While it’s indeed often due to "less-worrying" causes, it's better to be safe than sorry. Even minor chest pains can sometimes be a sign of coronary artery disease and clogged heart vessels - up to 30% of heart attacks have barely noticeable warning signs or symptoms.