Couple things you can try.
Change up the cardio part of your workout. It's similar to weight training. You should switch up your program every 6-8 weeks to shock the muscles, and it can work for cardio as well. Make sure to keep your heart rate in your target range. So if the majority of what you've been doing is running, start to ride a bike. or better yet, if your butt is the problem area start roler blading. Working the speicic part with the extra fat won't burn the fat off any faster, but at least you'll be toning up the muscle underneath, so overall it should look better.
Try interval training. You can find a program on the internet easily enough, but it basically involves jogging with intervals of sprinting. It basically teaches your body to sustain at a higher level, and really increases you fitness and can help the metabolism as well.
I think captn mentioned it. It could be that you are losing fat but gaining muscle, hence no wieght change. Feel your but, is it getting firmer? If so send me some pictures.....
.
Otherwise, don't worry, some people store fat in different places, men in the waist and stomach women in the thinghs and butt. Unless you go on a rediculous diet and training program to get your body fat down really low, it is possible that you will always have a little extra ghetto booty, but if your BF doesn't have a problem with it really isn't an issue. If he did have a problem with it there would be an issue, but it the issue wouln't be your butt.