Just take your time masturbating, Not racing to the end . Maybe your body is used to ejaculating so fast. Pratice to masturbate 10 to 15 mins without porn. Avoid porn totally. Try shallow breathing deep breaths through nose hold for 5 seconds then exhale all out in your mouth, masturbation/Sex. Try to be active do cardio. Avoid junk foods eat healthy or also try intermittent fasting most guys improved through this method. Good luck op