How can I treat sciatica naturally, especially at the stage of increasing numbness and tingling of leg?

Core Exercises. Typically core strengthening exercises are the best to help relieve pressure and forces in the spine. I would try and google some or look them up on youtube to see descriptions. If you can do them yourself, wonderful otherwise ask your doctor to get a referral to a good physical therapist for further assistance.
Stretching, exercise. You will likely need instruction by a physical therapist to learn the mckenzie protocol, but quite worthwhile to pursue. Also, there is a good chance that your protruded or ruptured disc might desiccate and shrink over a 6-8 month time period. But if increased weakness, muscle atrophy, uncontrolled pain, or problems with bladder, surgery is vital. Good luck.
Sciatica. Sciatica often improves after several weeks but usually there is associated aching pain. You may have a disk pressing on a nerve root exiting your spine. See a neurologist or neurosurgeon if symptoms persist or worsen and the appropriate tests and treatment will be ordered. Until then avoid heavy lifting or prolonged standing and , if you can take nsaids like advil, (ibuprofen) they may help.