Sciatica is usually caused by a dislocated spinal disc and should be treated by a professional, while lumbago tends to be due to muscle overload and can be treated at home. Differentiating between sciatica and lumbago is best left to a professional, but generally, in sciatica pain tends to shoot into the leg and straightening up is often impossible.
Lumbago can be treated with heat, e.g. using an electric blanket, gel packs or a towel rinsed in hot water. The procedure is similar to treating a stiff neck, only applied to the lumbar and pelvic areas.
As with a stiff neck, you can also try a massage to relax the muscles, but due to the location it cannot be self-applied. You lie down on your belly while your masseur presses a palm into your upper or lower back while massaging the muscles around the spine.