In conjunction with my book, for even FASTER healing I STRONGLY suggest you implement Dr Adam Story's stretches as shown in his videos below. He has many others which I strongly recommend, I have done many of his knee ones in particular and found them tremendous.
These are the ones I have found for the back. You will be able to find all his videos on YouTube.
THESE ARE THE LINKS HE MENTIONS IN THE ABOVE VIDEO: The stretch:
https://www.youtube.com/watch?v=AATJe...
The strength exercise: https://www.youtube.com/watch?v=Cbvbp...
How to tell you have piriformis syndrome: https://www.youtube.com/watch?v=kvPJD...