Hello Sir, I'm Vamsi, 21yrs Old. I Have Been Suffering

hello sir, i'm vamsi, 21yrs old. i have been suffering from chest pain for 1year since when i left my smoking. i feel chest pain when i stretch my chest part , when i contract my chest & when i sneeze.
the pain is persistent for 1year it is neither increasing nor decreasing. i'm feared of having lung cancer.
i smoked for 2years (10-15 cigarettes a day) & stopped smoking a year ago. since the fear of lung cancer haunting me i informed my dad about my problem. after having ECG, X-RAY, ECHO, TMT, ABDOMEN SCAN, FASTENTING BLOOD TEST(FBS). doctors said there is no problem at all.
but i did'nt get answer for the pain i'm suffering.
sir can you help me ?