One Day While Brushing My Teeth, I Gagged While Brushing

One day while brushing my teeth, I gagged while brushing my tongue and felt a pop in my lower back on the right side, followed by steadily increasing sever pain. My breath felt like it was taken away until I eventually collapsed to my knees and humped over on my couch. My breath slowly returned but I could not move my back with intense pain. The doctor did not want to do MRI because it is not believed to be a herniated disc. Date of incident was 12/27/2015. I still have pain in my lower back, right side whenever I am in an upright position for an extended period of time. The pain slowly increases over time. The only back pain I have had prior is on 12/23/2015 after working hard at work on 12/22/2015 I had a little back pain a couple hours after going to sleep from work. The pain persisted through the 26th and was almost completely gone. Then the occurrence I mentioned above happened.