Pleural thickening often occurs at the lung apices with increasing age, forming an apical cap. These represent a past infection more likely due to pulmonary TB, Fungal infections, asbestos. It rarely causes any symptoms and is generally assumed to be a benign and inactive process. Since you had symptoms and these findings are on CT scan, I think you should discuss them with a lung specialist or pulmonologist who can give you better guidance on how to proceed. The doctor would initially be following up with serial Xrays. Rarely, a biopsy may be requested to assess the tissue of the pleural membrane and to rule out such things as cancer. you should stop smoking and better visit to doctor and take appropriate treatment for your problem which is most necessary that time.