It's probably "piriformis syndrome." I think calling it a syndrome of a bit weird. Your sciatic nerve comes out of your spine and on its way down your leg, passes through your piriformis muscle, which can squeeze it and produce pain right there. If you don't do something, good chance you'll get a case of sciatica with pain all the way down your leg. "Do something!?" I had exactly the same thing (maybe exactly) this past summer. What I did:
First, my usual morning stretches:
https://www.bikeforums.net/road-cycl...l#post15372967
Then a set of McKenzie stretches:
https://spineone.com/mckenzie-method-back-pain/ I do these:
Then I did these stretches:
https://www.healthline.com/health/ba...sciatic-nerve?
The thing which helped me the most was doing for 3-5 miles brisk walks using a rolling hip motion where each hip travels in a circle as I walk. That seems to loosen up the spine or something(?) Worked though. Hurt like hell the first mile, but steadily improved during each walk.
Riding is really good, though. Every day. It relieves the pain, but unfortunately is not a fix.