Wow, a month since my last post and I'm still not completely fixed. It seems whenever I squat heavy, I hurt my back on one side or the other. I'm trying to figure out what's wrong so I can fix it, otherwise it's just going to happen again and again, but progress has been painfully slow.
One contributing factor might be one of my glutes, which knots up and causes some sciatica. That might cause me to twist to one side when squatting. To address that, I got my girlfriend to massage the area to loosen it up, which helped a lot, and I've been stretching my hamstrings and hips almost every day.
Another thing that might be contributing to it is weak abs, so I've been hitting my abs every workout, now switching to needsize 5x5 from a flat seat.
However, I started squatting a couple of weeks ago, got up to 115kg on Friday (my last PR was 135kgx5) and now my back's starting to hurt again.
*sigh*
There's a physio at the gym, so I've made an appointment with him for Friday. I'm sick of this.