The sciatic nerve is the largest nerve in the body and people suffering from sciatica have to deal with the pain and irritation of the nerve being inflamed. Sciatica is generally felt in the lower back, down into the back of the thighs, and even below the knees. Though a pinched nerve is one of the main causes of sciatica, things like tumors, internal bleeding, infections in or around the lumbar spine, and injury are big causes too.