I found it hard to self-motivate and "workout"....until I was taught to setup a "progress checkoff log"
I work out twice a week, doing stretch, treadmill, lifting weights, and weight machine routines. As I do each, I keep a checkoff list of each exercise, # reps, weight amount, duration, and outcome.
That way I can easily compare where I am vs. where I was. When I get "down" I can self motivate by seeing how I've progressed to date.