Thanks for the query to H.C.M. Forum.
As you clearly mentioned in your query that each & every reports regarding lung and heart are normal.
In my opinion this is a psychogenic problem.
Tension & work related stress
may be main cause. Anemia
is most prominent cause in this type of condition. Consult a psychiatrist
and get his opinion and treatment .
As you are young & doing hard work , so no chances of any heart or lung related disease.