[cabmandone]

^^^ Look up the "Cobra pose" and do it but not to the point where it hurts. Work gradually towards full arm extension. I think the one for the piriformis is called the pigeon pose. There's a variation where you lay on your back, put your left ankle on right knee and pull the right leg towards your chest. You can also so something similar from a sitting position leaning forward towards the leg. The pigeon pose is "advanced" but it's the one that helps me the most when I have a flareup. Another good stretch that I've used is taking a broom stick, holding it at the base of my neck and waistline, facing a set of stairs I put my heel on about the second stair and gently lean forward using the broomstick to make sure my spine stays neutral. This stretches the hamstring and calf. Remember to always warm up a bit before stretching.