I am male , age 34 and have been smoking since last 10 years. Recently I seem to feel a slight pain in my upper right side of chest after smoking. Had a x-ray done few months back but nothing came out. What can be a reason?

An x ray alone cannot determine damaged lungs from smoking. There are many ways and means of determining damage such as a sputum test.

Find yourself another doctor who knows the particulars of testing. The one you have does not.