Thank you forypur question This is a very common problem. it is called early ejaculation or premature ejaculation. There are many causes for this ranging from physical, psychological and poor masturbatory technique. Managing this calls for you to practice certain masturbation and relaxation techniques that help you to manage your arousal. There are medicines for this but their job is essentially the same - to decrease arousal. So it is preferable to learn the nonmedical techniques first and go for medicines if it doesn't help. try the book ' managing premature ejaculation' by Metz and Mc Carthy and see a sex therapist or psychiatrist if you are still no better. best wishes