Well the body does a lot of adjusting. The reason your gaining weight is all a science. I have the same problem and I workout. The problem is your body has gotten used to your eating habits. So your has trained it self to store weight instead of burning it. This doesn't mean your lazy or this is the body natural way of survival. If you want to lose weight. Start training and your metalopism will pick up. Then your body will in the habit of burning fat thus losing weight.