Ive had gastric byp..but im not losing that much weight?

I'm 18 and I had gastric byp March 29th, 2011. Its been like a month since and ive only lost 30 pounds. Ive heard people who have lost more in month then that, and they say if you eat something wrong or to much youll throw up or have dumping syndrome or whatever but I havent had any of that, I know I eat way less then I used to but I just dont understand why im not really losing anything. I also started going to the gym as soon as I was able to which was like the 4th week and I go TWICE everyday, So I thought I would lose more faster. Soo can anyone tell me why I havent been losing that much?