Hi thanks for asking question. Noted you have habit if smoking. So you could have smoking induced interstitial lung fibrosis or respiratory bronchopulmonary obstructive disease. Because of smoking there are also chances of emphysema or bronchitis that can lead to difficult breath. To differentiate between obstructive and restrictive lung disease pulmonary function test can be done. Stop smoking as early as possible. If needed steam inhalation can be taken. Biopsy taken along with chest x ray if needed. I hope your concern solved. Take care .