right buttock pain

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18KB, 267x400px

Whenever I'm squatting, after my 3rd or 4th set, I always get a mild pain (3-4/10) in my right buttock (red area at the img - at the top part of the glute next to the tailbone, but not on the actual tailbone). I even get this pain when I practice good form with low weights. The pain will persist for 20 minutes after I'm done squatting. I tried googling but I'm getting mixed opinions about what is wrong (can't tell if its a muscle or joint pain either). I get 0 lower back pain from squatting, no knee pain. Just that pain in that particular spot.

Anyone with a similar problem that can tell me which muscle/joint needs more stretch or more foam rolling? I've never snapped anything btw.