Running out of steam when you've got a carefully constructed plan for your next great business venture is high on the frustration scale. I've talked before about how working out your chronotype can help you make sure you're working on the same schedule as your brain. But there's always more to learn.
If you haven't already, try taking the personality test on the 16 Personalities site. It's free, fairly quick to do and their descriptions about behaviours, relationships and careers is invaluable.
See what you can find about the inside of your head. You'll be bound to find something useful to make your life more productive and less stressful.