It will vary what you put on from pg to pg for some women. It could just be that you are needing to eat all that food to keep you going so you are burning it off instead of turning it into fat, does that make sense? Many Drs etc don't even worry about weighing you so I think that as long as you are eating well, doing the exercise that you're doing and your check ups are fine, then I reckon you are going great guns. A friend of mine had her second baby back in Feb and she was a lot smaller this time round, had a smaller bump and she didn't gain anywhere near the weight she gained with her first one - not that she gained a lot then either, but the difference between her first bub and this one was noticable.