I'm in severe pain day n night all the way down my legs from my groin
My SI joints are frozen solid and still have that problem every morning. Seems to be the piriformis (see https://en.wikipedia.org/wiki/Piriformis_syndrome ). Piriformis stretch (ankle over opposite knee; push down gently) and diclofenac gel help. So does water aerobics.
Gentle Yoga helps
SI joints