I'm wanting to lose weight?

So, I'm not even 14 yet.. I'm losing weight super slow. I'm about 203 right now. This is bad. My goal weight is about 130. Since I'm pretty tall, just a little bit of pudginess won't bother me. But I'm waaay too overweight. I've been this way since I was little. I was always tye chubby one out of all my friends. I'm going into high school and I'm done with being the overweight one. I play DDR, walk my dog for.. 20 minutes everyday, and I drink plenty of water. How can I speed up my weight loss? I haven't been making much progress. It should take me at least 6 or 7 months to drop down to 130. Yeah, I wanna lose 70 pounds within 6 to 7 months. I don't wanna use any of that Acai berry crap, so please don't suggest it. I'm fine with doing exercises. Abd since I'll be going back to school soon, I'll have PE too so that might help. Is there anything/anyone that can suggest something to help me lose my weight in the desired time? Please and thank you.