Thanks for your question on Healthcare Magic.
I can understand your concern.
Since you are smoker, humidity can cause
bronchitis (inflammation of the airways).
And this bronchitis can cause
chest pain.
No need to worry for heart diseases as a cause for this chest pain because your
stress test is normal.
So
consult pulmonologist and get done clinical examination of respiratory system and PFT (pulmonary function test).
PFT will not only diagnose bronchitis but it will also tell you about severity of the disease and treatment is based on severity only.
In any case, it is better to quit
smoking as soon as possible.
You may need inhaled treatment also.
So consult pulmonologist and discuss all these.
Hope I have solved your query. I will be happy to help you further. Wish you good health. Thanks.