I had back surgery when I was 19 years old for a ruptured disc. Since then, every once in a while, I will herniate a disc and it starts to flare up my sciatica again.
There are actually a few causes of sciatic nerve pain
1. Scar tissue
2. Ruptured/herniated disc
3. Muscle inflammation
4. Tumor etc (Let's not worry about that one quite yet)
There might be more rare things, but these are the most common. The end result is one thing; something pushing against the nerve and pinching it, preventing it from moving freely within the nerve "sleeve". How do we fix this? Well, first, we need to figure out where the issue stems from. See list above. Second, we need to decrease possible inflammation that may have been caused. Thirdly, we need to get that nerve moving freely again. So, treatment could be first, fixing the main issue, either through physical therapy, surgery, rest etc. THe inflammation decreases through rest, NSAIDS and/or steroids, and the the third, through stretching to get that nerve moving.
If you have chronic issues with it, it might be a good idea to see a doc, then continue doing the nerve stretches to help prevent it from getting back again.
Hope this helps. I have become a freakin book on this subject. After PT, surgery, rehab, prehab, physical therapy, I have been through it all.