That's the thing, just setting realistic goals. It's good to push yourself, but not to the point when you're stressing about it. I'm a seasonal business owner. I work during the summer/early fall months, so I love the fact that I've got the time to do what I love!
I know the feeling about having your hands hurt, too. I have weak fine motor skills, and because of that I often find it sore to do certain things with my hands. Typing isn't the hardest, but after a couple of hours, they start to act up.