This is pretty normal and called premature ejaculation (PE). You have to give your wife an orgasm first before entering with oral sex or fingering her. That way it will be as much fun for her as it is for you.

There are various techniques for slowing down your orgasm - stop/start, contracting your pc muscles to stop ejaculation, thinking of something else, using a thick condom to desensitize you, using a desensitizing fluid and taking anti-depressants off label.