Maybe you can try other positions... there's a thread here
somewhere...
Here it is
Not sure how much information you can gleam from there
actually.~
An alternative is to try other types of sex, like you could have
her dress up, bondage, SM, ... haha.. you get the idea.
Read the kama sutra for more details ^_^
Hmm, i heard that Sex when the girl is angry can have some
wonderful results. You may want to give it a try, but be very
careful.
Sometimes its also due to heart-to-heart problems. Problems holding
you back. Maybe you'll do better after you solve them..