I have a rule about stretching and exercising, called the Rule of 80% effort. When your goal is to be healthy and increase your quality of life, there is no need to push yourself to your limits. 80% effort it more than enough.
If your goal is recovery, 40% effort is more than enough!
It's easy to get down on yourself when you can't maintain 100% effort. Americans feel as though they need to be pushing themselves as hard as they can whenever they are working. But often, this exertion only leads to fatigue, and then more disappointment when we just can't motivate ourselves to try any more.
If you feel like you are just not motivated, or are too tired, first, make sure you talk to a doctor or professional to make sure it isn't a symptom of something more serious. Then, try this:
Drink one glass of water, first thing, every day.
It sounds too easy to make a difference, but it's important. If you can get yourself to do one healthy thing every day, like drink a glass of water, soon you'll have the confidence to do two healthy things every day.
Not to mention, when you start being more healthy, not only does it make you feel good about yourself for committing to something, it makes you feel good in general because water is important for everything your body does. The more your health improves, the more you will want to keep improving and maintaining it. Start with small steps, then work your way up.
I do this all the time with my elderly patients when they first learn Up and Down Like the Moon and the Sun. Sometimes, they get upset if they can't even do one time up and down from the chair by themselves. Some people just quit. They are too embarrassed and too upset with their lack of physical health to continue. But others commit to doing whatever they can do without too much strain. I add yoga blocks to the seat so they only have to push themselves up a little bit each time. Slowly, over the course of a few weeks, they start lower and lower. Pretty soon, they are doing fifteen, or twenty times up and down from the chair with no problem.
So maybe you can do more than just drink a glass of water today, or go up and down once from your chair. How much you can commit to is like a muscle. You can't commit to a whole new routine in one day, so commit to little things, one at a time, over the course of a few months.
This builds up your commitment muscle, which is what you have to have before you can build up all your other muscles.