See the whole series of these at a harder world. Some images/language on that site are NOT SAFE FOR WORK. And the one with the penis? Well, if you want to see the rest, you will just have to deal with it.
I have found it helpful to do the stretching exercises my physical therapist recommends. Do some core strengthening exercises, such as the ones highlighted at The Mayo Clinic. By keeping your core strong, your back won't put itself in a position to cause that sciatica pain you are having.