It isn’t possible to have COPD in just one lung from cigarette smoking. When COPD is present it can be worse in one lung than the other.
Your symptoms suggest asthma. It is possible to have normal lung function tests with asthma, depending on the presence or absence of symptoms at the time. It could also be anxiety, with or without a panic disorder. Awareness of your heartbeat in your throat and the feeling of a lump in your throat can also be due to anxiety.
The report of a normal chest x-ray and lung function tests is very re-assuring. You should consult with a lung specialist to determine if you have asthma or a related condition. Also, there are many causes of shortness of breath, including heart disease. The longer you wait to seek expert opinion, the more anxiety is likely to play a role.