I have the same problem. I can be in a room and not speak and people still smell the odor from me. I also can only smell it through my nose not my breath. The smell can travel pretty far.
I recently did have an unusually long cold during my dental work. The doc said my sinuses were full. The funny thing is that I've never suffered any sinus infections.
Recently I went to a 2nd dentist to clarify the origin of my BB but she said it wasn't the mouth that was causing a problem.
Then today I coughed out tonsil stones. I too am wondering the cause of BB.