Back Injury from Squatting

Hi, today i was doing workout A of starting strength and i felt a ‘twitch’ in my upper back (about level with the bottom of my right scapula, just off centre) while doing squats. Now i’ve had this problem in the past with doing heavy squats (5RM, really struggled, eccentric and concentric were about 2 seconds each), last time i took a week off and returned and was fine. But i don’t want this to keep re-occuring as i would like to continue improving my squat. So i have several questions:

firstly, does anyone have an idea which muscle i might have pulled and what treatment aside from rest and ice (and seeing a professional) i could maybe do?

secondly, seen as this has happened before, is it likely to be related to form? I’m pretty sure i kept my back arched throughout the sets, so where else could i have gone wrong to create such an injury? Is this a case of my form not being solid enough with heavy (5RM) weights?

thirdly, would it be possible to do solely upper body workouts for a while assuming i’m feeling no pain?

By the way i’m about 6 1’, 190lbs male, been training about 6 months serious without injury, but not using squats. Today’s workout was the fifth workout of starting strength, this being the heaviest i’ve gone with squats at 220lbs.

Any help is much appreciated.