Don't get mad! But you do have a right to be frustrated. It's very common for girls to take a long time, have difficulity, or not even orgasm during sex. It tends to take more work to make a woman orgasm that it does a girl. You need to talk to her and ask her what turns her on and what feels best- do those things.

Also keep in mind that most girls cant reach an orgasm without clitoral stimulation (a lot of it!) so have either her rub her clit or you rub her clit during sex. You could also find positions that allow you to rub against her clit as you thrust (girl on top positons are good for that...)

Good Luck