Good day, either you are having stomach bloating, this will make you yawn even if you dont hurt, or you are just feeling blue, mabee a light depression, you know sometimes we feel the blues for no apparent reason. if it' not bloating and you check-up was fine, try boosting your system with good supplements, b vitamines will help a lots, and omega3 will give you lots of energy, hope you feel better soon.
Try to reduce stress and make sure you aren't overbreathing.
If your breathing is fast, try slowing it down and breathing out as deep as you can. Stress can cause you to midly hyperventilate, this would cause a decrease in the levels of carbon dioxide in your blood and allow your blood pH to increase causing symptoms.
Take some time out to mediate, relax, do things you enjoy and make sure you are breathing out for as long as you can.
Hope that helps, it ***** being so tired!