Hi Selym !!
read through your history .. Well What i fee is you could probably start with some kind of a piriformis stretch .. which would for sure be of some help.. ,most of the time since there is a piriformis syndrome, ppl tend to get this shooting pain like sciatica and ,the change is posture can merely be due to muscle spasm.. You could do a few reps of piriformis stretch along with gleuts stretch , and combine it with lateral bending to the opposite side of pain (contralateral side ) it would slowly hep in releaving the muscle spasm .
Hope that helps,
All the best ,
Radhika