I know first hand. the prednisone makes you yawn like a roaring lion. It makes me so crazy i cant take it.
I have a thyroid condition for more than 20 years. First, it was overactive. I was treated with radio activated iodine then it went under active. I have been taking Syntroid which is a hormones replacement drug. I have noticed that when my thyroid produces too much or too little hormones, i start having difficulty yawning and difficulty taking deep breath. As soon as my medication is adjusted, it goes away.
Get a thyroid profile test done. You could be having problem with your thyroid and you don't know it. It you TSH in your test is low, your thyroid is producing too much hormones. If TSH is high, your thyroid is not producing enough hormones and this can be your problems. It has been my problems for many years.
Hope this help.
Good Luck!
SuperBravo
My husband is a heart and lung patient, he has COPD from long ago chemical exposure farming, also sleep apnea. He says at times he has to yawn to be able to get a deep breath. Perhaps you should mention this to your family doctor letting him in on the new change you have now.