Is it mostly in the back, or does it go down the leg too? You could have herniated a disc easily. Even coughing can do that, cause I herniated a disc just by SITTING in a car going on a trip!!! I was just sittiing ---can you believe that? The first time, all I did was bend over to pick up an EMPTY laundry basket. And I was alone in the house, in the basement. I had lots of "fun" trying to get upstairs. LOL
Anyway -- You won't get much done at the ER. What you need is an MRI done of your lower back. The ER will just pooh-pooh it, and call you a drug addict.
Call your doctor and ask if they'll set up an MRI with and without contrast material. That's the only way you'll find out if you've got a herniation. They'll probably want to see you, but you can try by just calling. I'm sorry you're in such pain. Been there, done that several times. It's no darn fun.
PLEASE - keep us posted, ok? And let us know what the MRI says, ok? You can get a copy of the report for you to keep. Best of luck and God bless. Big hug, Lee