If you notice that your girlfriend is faking an orgasm, or if she does not, but you never see her body writhing in the way she should after all your efforts, then both of you should think about a way to solve the problem.
There might be quite a lot of reasons why no climax is reached during sex, and most of these are emotional ones.
Obviously, when there is a problem in the relationship, and the partners are not connected emotionally, their sexual bond will get weaker, as well. Problems will slowly lead to an emotional distance, which can even turn to anger at each other, and this is when they do not pay enough attention to each other in bed, so the orgasm will not be reached obviously.
Or, there might be a more simple reason, as well. If you lack excitement or at least a little variety, it is not likely to please both of you. Try new things in bed, or do it outside it, and this might solve your problem.
If your partner is shy, or if sex is embarrassing to her, then build up her confidence with showing your affection for her, and try to have sex in the dark. If this is her problem, then it will be solved.
She might be too young, or inexperienced, so she does not even know how to reach an orgasm. In this case, softcore porn or talking with an experienced woman is her best chance.
Unfortunately, she might have experienced rape or abuse, which led to a trauma, and if she does not see a professional, she might be unable to reach an orgasm in the rest if her life.
These problems can be easily solved, if both of you want it.