So, is this on the bike or in general? I'm not quite sure what you're asking about. My lower back is frequently sore but does not bother me much when I'm on my bike. It did earlier this season when I made some changes to my set up. I've since raised my saddle height and therefore rock less under effort and now it does not bother me on the trail. Gravity seems to bother me more now-a-days.

Another thing in general to do is core strength excercises. Things like sit-ups/crunches and all the various other mid-section movements should help. Of course, I don't know the extent of your injuries and whether is will help or not.