The sciatic nerve originates in the low back at L3 and travels down through the back of the legs. When this nerve is irritated, sciatica can develop. The sciatic nerve is the largest nerve in the body. Depending on where your sciatic nerve is being irritated will depend on where you are experiencing pain.

Sciatica can cause pain, tingling, or numbness that travels down the leg and even into the foot. It is a symptom of another medical condition, and not its own diagnosis. Sciatica can cause constant pain on one or both sides of the legs. Sometimes the pain makes it difficult to walk or stand up and has been described as burning or shocking pain.

Sciatica does not necessarily occur due to an injury, but can come about over time. The most common causes of sciatica are:
-Degenerative discs
-Lumbar spinal stenosis
-Sacroiliac joint irritation
-Lumbar disc herniation
-Isthmic spondylolisthesis
-Piriformis syndrome
-Pregnancy

Treatment of sciatica starts with identifying the medical condition which is causing the pain, and focuses on fixing that problem first. Sciatica is often treated non-surgically, so finding a great non-surgical orthopaedic physician is key. For many, symptoms will get better within weeks or even months. A physician may recommend medications, hot/cold therapy, epidural steroid injections, acupuncture, or massage therapy.

Sources
http://www.spine-health.com/conditions/sciatica/what-you-need-know-about-sciatica