This sounds to me like you need to have your back examined for disk and/or facet problems. Sciatic or related nerve irritation due to narrowing of the canal in your spinal cord sends out pain exactly as you describe. I know this because one year ago I was lying on the floor in pain asking someone to shoot me and put me out of my misery.
Those piriformis stretches work very well so by all means start as any physical theripist will include it and several other stretching and strengthening exercises. I can go on but my strong suggestion is to go get your back checked out. What you have may go away for a while if not properly treated but it comes back much worse each subsequent event. Feel free to contact me if you need any additional details.