I also did one of those crazy shoveling days a week or so ago myself.
I would be the first to say going to the ER and this is not my usual place to refer anyone,is a good idea. It sounds as if something could have gotten in a bind in some way. That stabbing burning kind of pain is usually associated with nerves in some way and that usually comes about when they are pinched off or compromised in some way. A Ct or possible MRI can find the culprit pretty quick.
Do you have a regular back Dock or PM Doc and if so it may get you faster and better care to try to make an appointment with them letting them know how much pain your in and the circumstances that brought it on.
Whichever way you go I certainly hope you get some relief soon and answers even faster.