I'm a competitive person, I like being good at things. Choosing a sport, basketball, to stay in shape has worked wonders for me. When I play basketball I don't think of exercise, or my tiredness, I just focus entirely on accomplishing the goal of developing the skills needed to beat opposition.

If you are boxing once a week, do you find it enjoyable? You could start being more competitive, starting with some light sparring and setting the goal of amateur fighting eventually.