If you're in pain, then a root canal is probably the proper treatment. It can be due to trauma and it may go away on its own but it seems to me that its not worth the suffering you experience when the treatment is given. Can they try a more conservative treatment instead of a crown, such as an inlay or onlay?
Check into material used for the temporary crown and/ or temporary cement used. You might be allergic to the components in it. (Try eugenol-free temporary cements)
Dr. Maksim Lyubarskiy
Dental Arts of Freehold