For a couple weeks now my progress in my squat has stalled due to a lower back/hip issue. Once I get up to sets over 275lbs. I get a deep pain in the right side of my lower back, right above my butt. It's unlike any other type of pain I've ever felt, it feels almost like a very painful decompression if that makes any sense.
At first I thought my form was just breaking down having not squatted in quite a while, but everyone I've had look at it says it looks fine to them, good arch, heels on the ground, knees strong and stable, etc.
So basically I've come up with two theories, the first being some sort of muscular problem in my right spinal erector from a hyper-extended lordosis posture, the second being some sort of horrible lumbar spinal injury, so my fellow athletes, any input?