Sounds like you might need to stretch your hamstrings. Hamstring flexibility is key to form in both squats and deadlifts. In particular, the hamstring must lengthen as you bend your knees in the squat, and it must lengthen as you bend over in the deadlift or you round your back, which is probably where the injury came from. Google "third world squat" for a good test of your flexibility. Most people have very tight hamstrings from sitting all day for most of their lives.

I'd pay for yearly clinics for compound lifts, especially if I could learn better form and better stretching techniques.