I don't know about rubs, but when I used to get a backache like that, a heating pad would work wonders. you can also do a yoga pose: kneel on the ground, sit your butt down onto your feet, roll your chest down onto your knees and stretch your hands out onto the floor in front of you, head down. it's called Child's Pose. here's a photo:
http://www.anusara.com/articles/columns/balasana.htm
that will stretch your lower back out a lot, so take it slow.
some pain reliever like tylenol might help. above all, take it easy! I feel for you. having lower back pain is the pits. next time make sure you lift with your abs and your legs, not your back.