Are you gripping your butt or lower back right now without even noticing it? Are you tensing your jaw, shoulders? (I have to remind myself every night to relax my jaw when I´m about to sleep).
Take a moment were you stop everything you are doing and just feel were you are tensing up. Then release and continue with your day. Do this 3 times today, and see what it brings. I believe this can possible prevent future or current aches and pains.