Is it a cardiac pain? Or some gas?

I am having a dull pain in the left side of the chest. The pain is present almost all the time since about 2 years, but it is very dull most of the days. Occasionally the pain becomes more and then becomes dull again after some days. Since last 2-3 days, the pain has increased again. It is present even while lying down. It increases when laughing or coughing. ECG taken a year ago showed partial RBBB. My bp is approximately 90/80 most of the time since past year. I am having mucus in my throat since past 2-3 days and spo2 drops to 90 occasionally. I am covid negative. Is the pain is more likely to be related to the heart or more likely related to lungs or related to bones in the rib cage or muscles or some gas? I am confused. Kindly help out. Thank you.