A few things. A lot of it comes down to nerves. If you're a virgin then for the most part you're nervous. You either can't get it up or can't cum. If you can't cum then I would suggest not masturbating for a week or two. The sensitivity will eventually return.

You could also be nervous. I mean you have to be aroused to cum. If you're pounding away and thinking about tax returns then no amount of pounding will get you to cum.

Change your mindset understand that it's a service. You don't have to be a Chad in bed with these girls. In fact all those ARs where the dude said they made the girl cum. It's probably not so.