Thanks for your question on Healthcare Magic. 
I can understand your concern. 
First of all get done CT scan of thorax. CT scan is more informative than chest x ray. 
CT scan will tell you if there is still pneumonia or 
lung abscess present or not. 
CT scan will also tell you if 
lung cancer is there or not. 
If CT scan is normal then no need to worry for lung cancer, lung abscess and pneumonia. 
Sometimes bronchitis (inflammation of airways) persist even after pneumonia is treated. 
Bronchitis can cause phlegm production and chest pain. 
So get done PFT (pulmonary function test) first. PFT will not only diagnose bronchitis but it will also tell you about severity of the disease and treatment is based on severity only. 
You may need inhaled 
bronchodilator (formoterol or salmeterol) and inhaled 
corticosteroids (ICS) (budesonide or 
fluticasone). 
Don't worry, you will be alright with all these. 
Hope I have solved your query. I will be happy to help you further. Wish you good health. Thanks.