I’m feeling discomfort in chest I did ECG and chest x ray all normal?

Hi I’m feeling discomfort in chest since the past few days especially when I’m lying down to sleep. I think there is also shortness of breath but I am not sure. I had chest pain for which I did ECG and chest x ray which turned out to be normal. But still m feeling discomfort in chest when I ly down. What can be the possible reason?whay test should I do?