It's possible, but your wife's situation is by no means unusual.

Be happy she can orgasm and you know how to do it. Use that to tease her and then to please her. Her not cumming during intercourse can also be psychological. Or you are a little too rough or maybe not rough enough. you penis might be too big and hurt a bit or too small and not hit the right areas. Try a few different positions, also use your finger inside her and have her tell you when it hits a spot that is sensitive. Once you know that spot you can try massaging it or try to hit it during intercourse in a certain position. Then again she just might not be able to orgasm with out clitoral stimulation. In that case there are some positions that will allow you to reach her clit and play with it during intercourse. One trick I use is to pull out after a dozen or so strokes and rub the head of my penis against her clit. Then back in, this usually does the trick with a hug climax. Something about the texture of the penile skin against her clit that feel so good for them.

Only if his penis is bigger than yours! jk...

you can try getting a sleeve,especially one that vibrates! http://www.edenfantasys.com/sex-toy-reviews/male-sextoys/penis-sleeves

I don't think a doctor will be able to help. At least a quarter of women are completely unable to orgasm from intercourse. Another half can do it, but rarely and perhaps with difficulty or additional stimulation - it is only one in four women that can achieve orgasm from intercourse easily and regularly! I never get why men expect it because it puts an unfair pressure on the woman and it is not her fault, it is simply that some women are different sexually to others. Often with a lot of experimentation women learn what works for them in order to achieve an orgasm during intercourse - often, for example, stimulating their clit during intercourse while on top, or only starting intercourse after foreplay when they are very close to orgasm. Some sexual positions also increase the chances - some women say doggy style works for them but it never has for me. The only position that ever helped me is the CAT position - it stands for coital alignment technique. You start off in missionary, and you lift yourself up slightly so the woman can put her legs down flat and put her ankles together. Then you lie on top with your legs straight and ankles either side of hers. This position lets the full length of your penis come into contact with her clit as you move, and also lets her tense her legs which may help her achieve orgasm. The CAT position can do it for me sometimes, but like a lot of women, and like your girlfriend, mainly I never orgasm during intercourse. Getting there takes so much effort it just isn't worth it to me, I'd rather have manual or oral stimulation to get me there. It may be your girlfriend is just happy with the way she is, in which case just please her in the ways she likes. If she wants to try, try the CAT position but don't make her feel like she is not normal and needs to see a doctor, or act like you really want her to, because she may feel pressured then, and most women are actually like her!