My question for you is, why can't you find the time or the energy? My guess is, it's because you're letting other people/things/etc. come first in your life. And while it's important to meet our obligations - you can't blow off work to run, no matter how nice the weather is
- it's also important to recognize the difference between activities that are "musts" (work, classes if you're a student, taking care of children if you have any), and those that are "wants" (and by this, I don't necessarily mean just things that you personally want to do, I also mean things that other people want you to do that you end up feeling obligated to do). I'll bet your "must" list is littered with things that aren't real "musts" for you, but are obligations imposed on you by (or that you've taken on willingly for) other people. Don't be afraid to stop doing some of those things, or to do them less. The world will not stop spinning if you tell a friend you can't go to lunch with her because you need to hit the gym, or take a night off from seeing someone you care about so you can cook yourself healthy meals for the week. The people in your life who love and support you will respect the boundaries you set, and those that don't respect your boundaries aren't the kind of people you should be surrounding yourself with anyway.
I know this sounds cheesy, but when you make your own health and well-being a priority, you will be amazed at all of the wonderful things/people it attracts to your life. So many of us - women especially, I think - have had it drummed into our heads that it's "selfish" to put ourselves first, that we're only worthy when we're serving others. That, frankly, is cr@p. You can't be the most successful, most fully realized version of yourself without taking care of yourself, so don't be afraid to make YOURSELF your number 1 priority.