This has been bothering me since March and basically has taken all the fun out of running for me lately. How long did it take you to fix yours, and can you post a little more about your routine, such as reps, etc? I just got over some serious ITB issues that kept me out of running all fall and winter, so I finally healed up around January/February and got to run pain-free for a little while before this piriformis thing came out of nowhere. I bought a lacrosse ball to sit on last Saturday and so far I think that might be helping.
I developed my PS during my half-marathon. I ran on my ITBS and it altered my stride enough that it caused too much stress on my piriformis, which likely was weak.
After my half, I took a week off from running. I walked on the days I typically run. I also started side leg extensions (10 reps/side, 3 sets) with resistance bands and one-leg squats (10 reps/leg, 3 sets). I rolled my entire left leg twice a day for over a month (30s each of glute, hammy, quad and ITB x 3). For the piriformis, it involves sitting the affected glute on the roller and rolling diagonally. For stretches, I did 3 reps of 30s for cross-leg ITBS stretch and 3 reps of 30s with hip flexor (lie on back, bend affected leg at knee and pull over other leg - I can try to find an example if you'd like).
It took about a month for the pain to go away. Sometimes, I can feel my piriformis towards the end of a 10 mile run, but it doesn't really bother me anymore.
Today, my exercise routine looks like this.
Run Days
3x30s toe touch stretch
3x30s heel drop stretch
2x30s cross-leg ITBS (don't think stretching really helps ITBS, but w/e)
3x30s hamstring stretch on back
3x30s hip flexor stretch on back
6x20s Supermans
Weight Days
A:
bent over row 3x10 / arm
standing triceps extension 3x10
standing upright row 3x10
Arnold press 3x10
resistance band side steps 3x10 steps / leg
lunge with torso rotation 3x5 steps / leg
clamshell with resistance band in side plank position 3x10 / leg
bridge plank 2x45sec
one-arm plank 2x20sec / arm
bicycles 3x10 / leg
B:
bench press 3x10
pullover 3x10
concentration curls 5x5 / arm
weighted squats 3/10
resistance band side steps 3x10 steps / leg
clamshell with resistance band 3x10 / leg
straight arm side plank 2x45sec / side
one-arm plank 2x20sec / arm
bicycles 3x10 / leg
Let me know if you want any more detail / clarification on my routines. Don't forget when you're building muscles (strengthening your weak muscles), you're getting enough calories and protein.