Premature ejeculation is most of the times is due to psychological reasons. As you say you are suffering for very long time . I would suggest to seek counselling
from expert which will help ypu both.
Certainly some test may be required then proper therapy may be given some local application and drugs like Dapoxitine 30 mg to 60 mg may be used 1 to 2 hour before the act. hope this will help you .