I find alternating the type of exercise to be helpful too. If I had to go to the gym 7 days a week, I'd get really bored. So instead, some days I hit the gym, other days I practice my drums (playing fast metal / punk so I'm tired and sweaty when I'm finished).
Exercise is amazing, once you have done it.
I try to get myself to exercise (run or gym) at least 4 days a week, but some days are harder than others.