Feeling tired last 3 weeks. Some difficulty of breathing or prefer to take frequent deep breaths. Headache and very mild infrequent chest pain. Reason?

Multiple symptoms. You seem to have multiple symptoms, you may need to get checked with your doctor, to get to the bottom of it. Good luck!
Heart/lung disease. Difficulty of breathing means the body wants to make up for diminished oxygenation from poor transport of oxygen from alveolar air to pulmonary capillary bed. This maybe due to congestion in the lung or bronchial spasm. Lung congestion may mean heart failure thus more water in the lung. Bronchial spasm maybe due to infection or bronchitis or emphysema. See an md sooner than later.