Slight limp and chronic lower back discomfort (but no pain) from doing deadlifts. how can i prevent further pain?

It's not right!: You're not supposed to limp from deadlifts! you're supposed to feel morally superior, but you aren't supposed to suffer. Ask your trainer about your technique, and back off this exercise until you've had a chance to talk with your doctor. You may still be able to do activities like the elliptical, the recumbant bike, etc., so don't give up altogether.