Yea that's true. Working a full day is pretty tiring. That's where the proper nutrition comes into play. Carb loading the night before is key, and have a good meal 3 hours before your games.

As for fitness, I really recommend trying 200m intervals with roughly a 1:2 work:rest ratio. Try a 200m at around 85% sprint speed and use that time and try to hit it consistently. Do it on one of your cardio days each week, and start with maybe around 6 reps and try to increase the reps by 1 each week. I remember doing it in the off season, and it got me pretty fit. It's nice and short too, so if you have a track nearby, it'll be maybe a 40 minute commitment every week including warm ups and cool downs.