Does Persistent Back Pain Indicate Herniated Thoracic Disc?

I have pain in my mid back, well, closer to the higher portion of my back then lower. It has been like this on and of for awhile now. I had a thoracic mri done about 2 years ago and there was a bulging thoracic disc at that time. How do I know for sure if that disc has not herniated? The pain has been constant for 4 days already and nothing I do or medicine I take relieve the pain.