is most of the time psychological rather than organic problem
You can get some antidepressant prescribed by a psychiatrist
to treat this problem.
The first and foremost thing is that you need to relive the stress
related to premature ejaculation.
Dont think of ejaculation during intercourse. Some doctors suggest 1to 1/2 hour before masturbation
prior intercourse, this can increase ejaculation time later.
Eat healthy, do mild cardio exercise and some yoga.