Could it have been the squats?
I just did 270 pounds of 5/5/5 squat today. Until today I was never sore after workouts (only exhausted), but my hamstring got sore after today's workout. I don't think there was a change in form that may have caused this, and I've been eating a lot with GOMAD and tried getting as much sleep as possible, so what do you think could have triggered it?
Could it have been the squats?
I've been squatting 3 times a week for a while, and have never been sore due to the squats until today. That is why I find the sudden soreness odd.
I'm not the expert, but could be as simple as a pulled or strained muscle. Foam rolling works wonders for me in that case. If it is just a muscle, its usually ready to go by the next lifting day for me.
You got sore after doing squats? You might want to have a doctor take a look at that. It could be serious.
maybe the first time you did parallel-squats and not half-squats ?