As a follow up, I think I found the source of my recent pain when squatting.
At about 1:20 in this video he shows a technique for the hip flexor:
I have been experiencing strong pain on my right side at the bottom of a parallel squat recently. Knew it was my hips....did an ass load of stretching over the last week and no improvement.
Stuck the lacrosse ball on my left side tonight, didn't feel much pain. Stuck the ball on my right side where the squat problem is, and holy shyt it hurt so bad
Gonna do this drill nightly and hope that in a few weeks my tightness starts to go away