Back pain can be caused by a wide variety of factors. Too much sitting or leaning forward can certainly increase your chances for back problems. Watching your posture and taking short stretch breaks every 10 or 15 minutes may help. Try to keep your chin from sticking out like a turtle. Keep your shoulders down and back, and use a chair that puts a small arch in your low back.
You may want to consult a physical therapist. The therapist can check your posture, workstation, and the strength of your back muscles. Six weeks of specific exercises for your back combined with increased activity may be recommended.
Diseases such as cancer, ulcers, brittle bones (osteoporosis), or kidney infections can cause back pain. You should see a doctor if making some changes in your workstation and increasing your activity level do not change your back pain. If there is any blood in the urine or stool, numbness or tingling down the leg, stomach upset, or other unusual symptoms, see your doctor immediately.