Muscle doesn't actually weigh more than fat. It's more dense than fat and takes up less room. So you can weigh more and be a smaller size than someone who doesn't exercise. But what you are experiencing is most likely muscle edema. That is when you workout hard and your muscles retain water to help them heal. The muscle fibers get little tears and water helps them heal. So it can show on the scale as a temporary gain, no loss or small loss. It is temporary. Just because you don't see changes on the scale, doesn't mean there aren't changes happening in your body. You can lose fat and not see the scale move. Google "why the scale lies" for insight in to water weight. Consistency is key. So just keep going and the scale will catch up. You are doing great.