Back pain is often a symptom of tight hamstrings. Buy a lacrosse ball and take it to work. Use it under your glutes and hamstrings throughout the day to work on your mobility. Just sit on the ball and move around until you find a tight/sore spot then work it for 10-15 mins. Once its pain free, look for different spots or switch to a different muscle. If you do squats or sprint workouts, doing this the day after those workouts is awesome.
Using a lacrosse ball at work will be less effective if you have a super cushy office chair. If so, try and get a fold up chair in your office/workspace to use with the lacrosse ball throughout the day. Or use it on your desk or a table, or even the floor if you must. An added bonus is you can stand up, put the lacrosse ball on the edge of your desk, and use it to rub out your quads as well.