Wow, I understand where you're coming from,(what guy doesn't want the girl to cum due to their cock?) but everyone else is right. You're putting way too much emphasis on it especially since how important the orgasm from intercourse is is totally dependent on the girl. Some girls regularly orgasm from normal intercourse. If I remember correctly though, those girls are the exception. For the rest of them (the majority), the orgasm from vaginal intercourse is rare and orgasm is more almost always gotten by clitoral stimulation.
You'll be surprised how little the "orgasm caused by the penis" matters to women in the end. Will they like it? Of course. Will they think you're bad in bed if you can't do it? Of course not if you're good in other ways. Heck, I've been with a girl who never had an orgasm with me (from intercourse or oral sex) but yet would rave about how great I was in bed and be constantly trying to find time to hook up. A couple of girls (including the one I just mentioned) I was with have told me that they rarely ever orgasm from intercourse. The other one told me basically it was quite rare and it usually happened for her only when she was helping (ie rubbing her clit too).
In the end, it's good that you know it IS your problem, but honestly the only advice I can give you is
1) Don't ask about her sexual past. How good her old partners were, how big they were, if they made her orgasm with their cocks.
2) Don't CARE about her sexual past. If she rather be with one of her old partners over you, then she'd still be with them.
3) Concentrate on making sex enjoyable for her AND you.
4) Remember the goal is NOT "make her orgasm with my cock" but it's "make sex as enjoyable as you can for her AND you". People are trying to snap you out of it because you're just on this path to making sex suck for you and for her and it's just stupid. Not only are you going to ruin your own enjoyment but hers too?