You've gotten some good advice already, but I thought I'd chime in too.
I have a (long) history of sciatic problems so here are some things that have helped me.
Keep up low/no impact exercise, it really helps to stay active at whatever level doesn't cause more pain. Walking and swimming work well for me. The worst thing I've found for back pain is inactivity.
When you have an acute episode of pain, icing the area for 20 minutes or so can really help a lot.
A really good stretch for sciatic pain is the one where you sit on the edge of a chair and cross your ankle over your knee. Put a little *gentle* downward pressure on your knee. I do this multiple times a day, even when my back is behaving and it really seems to help keep things loose.
Strength training exercises for your abs and lower back will help a lot but be sure to ease into them very slowly so as to not cause further injury (I learned this one the hard way) Never start up new exercises while you're in acute pain.
I hope you feel better soon. Backs are such tricky creatures!