I don't know if this will help, but I read somewhere that one of the big problems with quitting smoking is our breathing. When we smoked we would sit and deep breath for about 7 minutes. The act of inhaling the smoke and then exhaling it was very relaxing to the body. When we quit smoking, we don't often do this anymore. I have found that when I run, I have to do a couple of those really deep breaths a few times. I don't know if this has anything to do with yawning, but maybe try deep breathing a couple times throughout the day.
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Trouble Yawning 
