What Causes Breathing Sound In Ear?

Hello, I recently have gotten over an infection in my ear and went to the doctors twice after it was gone because of a "breathing" sound in my ear. When I told my doctor he said that there was fluid in my ear and a decongestant should clear it up. It did, but about 4 days later the sound came back and I went to the doctors again. He said that he couldn't find anything wrong with my ear. There is no pain just the "breathing" sound, which varies to almost non-existent to loud enough to wake me up from my sleep. Is there anything else I can do?