My first root canal was Hell! Utter hell. And in reading what you're going through it's almost exactly the pain that I went through. I know this may not help, but sometimes the pain medicine that is prescribed makes the pain worse. Especially Hydrocodone.
While I was serving in the US Air Force during the 60's, I had a root canal done and experienced pain much like yours. I went back to the dental clinic and was told that the tooth needed to be filed down. On my third visit, x-rays were taken and I was told that while removing the bad nerves from the tooth, good nerves were damaged. Another root canal was done, and this time I had no pain or problems.
Good Luck, with your ordeal.
Carolyn44