I went through the same thing. I had a very hard time maintaining my weight. Because of other complications, my doctor told me he needed me to gain weight (even though I'm still overweight--204 before pregnancy). I couldn't do it with the band, no matter how hard I tried (and, believe me, I got SOOO tired of eating!! How weird is that!)
At about 20 weeks, my band tightened and I couldn't even keep fluids down so I went in for an unfill. Well, turns out my port was flipped.
They had to do surgery (no anesthesia!) to rectify the situation. I am now 26 weeks pregnant and have gained about 21 pounds. It's on the high side, but I'm not TOO worried yet. We'll see how I feel when I get closer to my due date (February 25th).