The sciatic nerves are actually bundles of many nerves branching out of the different levels of the spine and form two branches that run down each side of the low back. Lack of fitness creates weak, shortened muscles that press on the sciatic nerves and cause constant pain. Exercises to stretch and strengthen the muscles can be very helpful. Sitting for prolonged periods can also cause back pain to flare or worsen due to poor posture. Try to sit up straight with your shoulders back and your lower back supported with a special chair, a rolled towel, or pillow. You should also try to stand and stretch every so often.