Core Exercises. Typically core strengthening exercises are the best to help relieve pressure and forces in the spine. I would try and google some or look them up on youtube to see descriptions. If you can do them yourself, wonderful otherwise ask your doctor to get a referral to a good physical therapist for further assistance.
Yes. Especially if it is due to piriformis syndrome. If it is due to an irritated nerve root, stretching will heko in the long run, as will core strengthening. However, sciatic pain can be from a herniated disc and you should speak with your physician first if any stretching makes it worse or if you suspect disc issues.