I had the same thing, I always figured it was because they stuck me four times!! Sometimes,even now, three years later I feel a twinge and I get low back aches frequently. A year after I would still have significant pain at times. I usually do some stretching to help. A great one that helps me is to get on all fours and arch my back up like a cat while inhaling, then dip it down and exhale. Also you can lay on your back with your arms laid out horizontally on the floor and lift your knees up as if you were going to pull them to your chest but drop them down toward your left side while looking to the right then reverse if for the other side, if you google "torso twist" you can probably find a picture of what I am talking about, that stretch is awesome. But if you just hop online and look up "low back stretches" you should find some good ones. Anyway, not sure if it is "normal" but I had it and short of going in for an MRI, don't think the dr can do too much. So I just manage it if I have pain there and try to stretch it out. If you think about it right after having your epidural you began to carry a baby who was increasing in weight and putting extra pressure on your lower back, that is what I have always figured was a big factor. Best wishes!!