The solution is to vary your activities. Walk one night, cycle another. Also find variation in what you do. Take a different route on a walk, or set markers ahead of you and see how long it takes you to get to them. Keep track of progress.
Improvement is great motivation, so keep track of it.
This could be how long an activity takes, how long you can do it, or just how you feel afterward. Develop a system and keep track. Not your weight, your attitude. Nor do you have to work too hard. Don't give up.