4 1/2 Post-Op And Not really Losing Weight

Help Guys! I'm new to this so I'm still figuring out how to use this. I had the lap band surgery done on 1-22-13. Since then I've had 4 adjustments and do not really feel much of restriction. I'm currently filled at 6.5 cc's and the nurse advised me that most patients stop at 7 cc's even though my band can go up to 10. My last adjustment was this Tuesday, and I'm barely feeling a restriction. I have lost 19lbs since my surgery but I feel it's only because I've been eating healthier and less food while working out at least 3-4 days a week for 2 hours each day. I feel like the band hasn't helped me lose weight and it's frustrating me so bad. My sister had the band done 2 years ago and is now at her weight loss goal. She was a little heavier than me but in her first month of being banded she lost 40 lbs while I only lost 3 lbs. She never exercised in the last 2 years and didn't make the best food choices and still lost weight so I don't get what I'm doing wrong. I know everyone's body is different but any advice will be greatly appreciated.