You're setting up on your heels and your shins are too vertical. Get the bar across midfoot, then sit your ass down until your shins just touch the bar. Then make sure you're on midfoot before you set the back. Because of your setup your quads can't help as well with breaking the bar off the ground, so you rock back more and open the hips to get it going and then make your low back work harder than it has to.
If you can fix your setup and break the bar off the ground by extending the knees, you'll get a straighter bar path, a more efficient deadlift, and a happier back.
On a side note, completely laying off for a week is not a good strategy. Doing some lighter squats the next day or the day after would be a better course if you suspect it's your technique on the deadlift that caused the issue.