Stella, I am sorry to hear this.
Same thing happened to me several years ago deadlifting. My guess is that you crunched a disc in your lower back. You definitely need to see the chiro ASAP. WHen it happened to me, I was stupid and ignored it for a few days, and I made it way worse by training until it seized up completely and my husband had to carry me to the chiro and I had to walk with a cane for a week.
I'm concerned about all of the heat recommendations. Right now, I think you need to ICE it. You should ice an injury for at least the first 48 hours or so to reduce any swelling or inflamation, especially if you don't know what exactly is wrong.
http://orthopedics.about.com/cs/sportsmedicine/a/iceorheat.htmYou should also see a doctor if you think it's a real serious injury, but unless something is torn and needs to be replaced or re-attached, the doctor isn't going to do much for you but medicate you. Nothing wrong with that, of course.
When I hurt mine, I probably could have seen the chiro and recovered in a couple of weeks. Instead, I was carried to the chiro and it took about 12-15 visits and 3 months to recover.
Keep us posted...I hope you feel better!!