Second the advice for you to post a video so we can critique.
I am also not a huge fan of Starting Strength, especially for somebody who's been lifting for two years and gotten used to higher volume training. The solution might be to do low volume squat work 2-3 times a week (leg days, + warm-up for an upper body day), and grease the groove of the lift so to speak.
On the other hand, if you're doing it wrong, it won't matter, so post a video :).
I am guessing you are relatively long limbed, as your deadlift number is definitely not terrible and is indicative of someone who has spent a good amount of time training their posterior chain. Long limbed people tend to suck at squat more and have to work at it harder, including lots more upper back/lower back work, and more variety in assistance lifts. I would change a portion of your assistance lifts to things like lunges and step-ups, and bulgarian split squats. This will train the squat pattern more while also still training your hamstrings.
You probably need a lot of ab work as well to keep from caving over.