What Do You Do to Avoid Burnout?

Somewhere in the past two weeks, I've hit either a workout wall or some kind of mental burnout in swimming. After finally completing 2000 yards (I am a natural sprinter, so I STRUGGLED), I quickly went downhill, first hardly breaking 1200 yards, then 600 yards, and last week, I had to get out at 150 yards. I'm not sure if it's because I started cross training in kickboxing or whether my workouts now fall in between me teaching two to three swimming classes in a row, or what, but I just feel burnt out and unmotivated (and now that the high school swim team has started practicing at the same time I begin laps, I feel even less motivated! :( ) Any suggestions on keeping my spirits up and getting past this burn out wall?