I know that rear-end collisions usually result in neck or upper back injuries, but I have suffered lower back pain in the wake of my accident. Could this be related to whiplash?

Yes. Lower back pain has been found in 34-42% of whiplash victims and it cannot be assumed that any pain or injury that you feel after an accident is unrelated to the crash itself. Regardless of the type of pain or on what part of the body it is felt, all injuries should be treated as seriously as any other and checked accordingly.