You might be better served by posting in the SS coaches forum. But just a few comments to help you along won't hurt. I hope.
You are 175 lb at 6'3" - that's light for your height. Unless you are a naturally strong freak, you need to gain weight in order to lift heavy, one way or another. Also, being so light at your height is probably not helping your back.
If I'm not mistaken, judging from your head position you're looking in the mirror while squatting. This is not good. Look down. DOWN. Down, as in on the ground, maybe two or three feet in front of you. DO NOT LOOK IN THE MIRROR.
Also, your knees are all over the place. Shove them out. Really shove them out. And keep them shoved out. You may need to widen your stance a little bit and see if that helps keeping the knees out.
A related question to your back: are you deadlifting?