I would just ease off the weight a good amount, work on getting your form exact. I mean that's what I would do. When I go in and my lowerback stiffens up real bad and can't really push it. I'll make my workouts more productive e.g. work on form, get some mobility drills in, do alot of foam rolling.
How are your glutes firing? I know if your lowerback feels like it's taking more punishment then it should you might need to acknowledge your glutes/hamstrings aren't compensating enough thus putting more strain then necessary on your lowerback. big strong ass/hammies = bigger weights