I have a sciatic nerve acting up, how can I relieve the pain?

Conservative care. Lumbar radiculopathy, or sciatica, can initially be treated with exercise and stretches as part of a physical therapy regimen. If your symptoms persist, you may be a candidate for lumbar epidural steroid injections to decrease the inflammation around exiting nerve roots. Any associated numbness, weakness, or incontinence merits urgent medical evaluation.
Depends on cause. How to relieve it depends on what is causing it. In many cases, sciatica responds very well to osteopathic manipulation. That would certainly be a good place to start. Ultimately, you need to know what is causing the problem to know how to treat it.