I don't see anything wrong with going to the ER... explain what's been going on and that the nurse at your docs office blew you off, that your doctor is booked and you're scared.
I don't see anything wrong with getting it checked out... at least get some reassurence and not have to wait it out all weekend. The stress isn't good for you honey. If it gives you a peace of mind, then DO IT! Take care of you okay?