How Do I Get Him To Go Down On Me?

I've been dating this guy for about 4 months now and we recently started having sex. It was my first time but I'm everything BUT shy when it comes to my body/sex. I've given him head several times and he finishes every time we have sex, but I have yet to orgasm with him. I want him to go down on me but I don't know if he hasn't, because he doesn't know if I want it, or if he just doesn't want to?? Should I restrain from getting him off until I orgasm?