Most likely you will not build muscle with what you are doing. Boxing is an aerobic activity for the most part. And protein is not a magic formula that you eat or drink and it leads to bigger muscles.
For your muscles to grow, you have to make them. And to make them, it takes hard work through overloading each muscle with weights that they are not used to. They grow because you break them down with weight training. Our bodies are very smart, and the muscles want to grow and get stronger so they can handle what you throw at it next time. It is almost like a form of evolution.
Short answer, add weight training.
