Low back pain is extremely common and is most likely due to tight hamstring muscles in the back of the thigh which result from sitting. The angle between the thigh and calf should be less than 5 degrees. However, the more you sit the greater the angle. The angle between my thigh and calf was 14 degrees before I started to exercise. By getting flat on the ground with a pillow or yoga block behind your head you can stretch your hamstring by placing your foot against a wall or pole as I did here. Spend about 5 minutes stretching each leg and then you can also do a split to stretch the inner thigh muscles while on the floor in the same position.
I used a pole to be able to go into the supported squat which opens the hips. This can be done by supporting yourself on a door jam or a pole as I did. Slowly go into a squat supporting yourself even if you back is uncomfortable.
To prevent back problems, it is important to strengthen your core muscles. Here I am showing a plank exercise on a ball. Keep your abdominal muscles tight and move your elbows forward and back without moving your feet. Do about 20 reps.