I know how that is. It's happened to me a lot, I won't exercise for a day, then the next day I'm unmotivated to, and then it turns into not exercising at all. Just remember all the hard work you've done, and that it really isn't so bad to exercise for an hour a day or so. That usually helps me out. Today I was feeling really unmotivated because I gained weight, but I still went anyway, and I'm glad I did because I feel a lot better now.