I had this issue 3 years ago that kept me out for a couple of months. Went to the chiropractor 4 or 5 times and then stopped as I felt it was beginning to aggravate the issue more than helping. Stop skiing for a few weeks minimum to let things "settle down" and to build strength. Started sleeping with a pillow between my legs since I sleep on my side. I also began doing dead lifts (not heavy weight) over the off season along with once every two weeks during the season using a hex bar to reduce the load on the lower back and have been symptom free ever since. Make sure your lifting form is perfect however. I also recommend McGill's books, especially the latest.