Piriformis pain sucks!!! I hope I can help you.
I experienced it last indoor season amidst a training cycle and racing period in which I was feeling incredibly fit and confident. Hence, I probably pushed my workouts too hard the week following a pr. The inciting factor was fast track work on a not completely rested body. Sooo, just as with any running injury, REST is imperative and underrated.
The pain would bother me so much and I limped around like something was up my arse for at least a week. I constantly foam rolled, and rolled out on a lacrosse ball (very good to dig in deep at specific spots), but honestly to no real effect other than short term relief. Honestly I believe too much foam rolling and working of the muscles doesn't let them rest and heal on their own enough, so in that regard, I would recommended to not foam roll too much.
Just as you stated, my athletic trainers had my work on fire strength excercises such as donkey kicks, fire hydrants, clamshells, and glute bridges etc for a few weeks after the injury started. These excercies truly did help restore my strength and muscular imbalances in my hips/glutes. Continue to do these even after you move past the pain and resume your normal training. It is great maintenance for the body.
However, the most helpful pain and symptom reliever for my piriformis came from searching stretching excercies on YouTube. Just look them up. I started doing them and felt immediate relief from the deep stretches they provided. Do this.
Once I took some time off, I resumed training. I ran lower mileage the rest of the outdoor season. I started doing 50-70 as opposed to the 80-90, and just relied on my previous fitness and confidence to carry me through.
I hope it works out for you! Rest well- sleep on a good routine at an early hour. Hydrate better. Do the excercies. And take a little step back from running, relax, and sometimes remaining patient is the only thing you can do. When I recovered from my piriformis pain, I had the best outdoor season of my life! Good luck brother