Are you both females? Your site says female, age 15 and you said girlfriend. So if you both are, is she returning the same kind of sexual favors you are providing her, great sex comes from great conversations. You need to tell her when she is on the right track, what track you would like for her to be on, and if she is doing somthing you don't find good. By talking during, before, and after not only will your sex life become better, but your relationship too. good luck
i really hope she's on b/c and you're using condoms...other wise you could end up with std's and an unwanted pregnancy.
You are much to young to be having sex. Maybe it's your body telling you to slow down. Good things COME to those who wait.Please practice safe sex the mistakes you make today could last you a life time.STAY YOUNG DON'T TRY TO GROW-UP SO FAST you have plenty of time for this kind of a experience.:)