As Kaitlin said, spine stuff takes priority and all that, but as far as your hip-to-knee pain goes, have you considered that it might be as simple as a strained sartiorius?

Consider for a moment the function of the sartorius, which is hip flexion / abduction / external rotation (basically the bottom position of your squat clean). If you are actively pulling yourself into the bottom to drop beneath the bar, it seems likely that that sucker was firing and doing some work. Your crappy rep might have caused some issues there.

Also consider the fact that you were sprinting on the same day. As you extend that leg and internally rotated, dear Mr. Sartorius is going to be put under stretch, and then I would suppose it is active in driving that leg back forward.

I guess it really depends on whether that pain feels “nerve-y”. Just an idea, really, but it seems to make sense. If your back isn’t too jacked up, and provided it doesn’t cause any sketchy pain, maybe try some cautious smashing of the flexor wad and thigh.