Worried and Confused

My name is Renee. I had gastric bypass surgery back in October 2006. My surgery went well, and I dropped approx. 90lbs, before I found out that I was pregnant in April 2007. I am now 51/2 months pregnant. This is my second child. My first was before I had undergone surgery. I have maintained the same weight since I found out that I was pregnant. I figured I should probably gain a bit more soon. My measurements are good my ultrasounds have been good, and the baby's heartbeat is good too. I have lost almost 10lbs in approx. two weeks. I am a little worried.