Your problem is Premature Ejaculation and not Erectile Dysfunction. Premature Ejaculation is the most common sexual problem experienced by man.
There are certain techniques, which can help you to stay longer.
Kegel exercise is one of the very popular and effective techniques to control premature ejaculation. These are the exercises of pubococcygeus muscles (PC) muscles. A man can do these exercises anytime and anywhere and no one will even know about it. To identify the muscles of your pelvic floor stop your flow of urine next time you go to urinal. Contract the muscles tightly holding for 10 seconds i.e. stop urinating inbetween. Do this thrice a day repeating 10 times. The PC muscles control the urine and semen and firmness of your organ during erection, so keeping them strong will increase ejaculatory control.
If you are married then squeeze technique can help you. While having sex when you think you are at the point of coming, ask your partner to gently squeeze the head of your organ. This will help in delaying the urge to ejaculate. A little practice will help get the right pressure.
Sometimes it is helpful to masturbate an hour or two before having sex because a second erection afterwards usually lasts longer.
Even feeling and touching other parts of the body during sexual act avoiding intercourse can be helpful to remove pressure from your sexual encounters.
Simple change in the sexual position which is less stimulating (female up) may also help.
Certain medicines eg. SSRI, local anaesthetic cream and condoms are also useful.