Read about Liver Chi stagnation. It's a Chinese medicine thing.
In short, it sounds like your blowing off excess acid.
Body wastes are removed as follows (don't remember the exact figures but this is very close)
4% of body waste goes out as urine.
6% goes as crap.
19% goes out as perspiration (or skin breathing).
69% is breathed out the lungs.
Clearly, breathing is more effective than crapping, hence exercise regularly. It's not an option, as you can see. And also do yoga and/or meditation for breathing.
Here's what seems to help the most...
No greasy, fatty foods for dinner.
No refined flours for dinner, i.e. heavy bread use, pasta, etc.
No eating past 6 or 7pm.
No desserts past 6 or 7pm.
All of these are big acid producers.
Never stuff yourself for the dinner meal, take it easy, try soup and salad, and go easy on bread.
Chinese medicine says the liver needs to clean blood between 1am - 3am, so digestion must be well finished before this event, else it doesn't go well and you will carry blood toxins into next day, builds up, and so on.
Your body is yawning to expel waste. You might be sighing more, too.
I know a Japanese guy who says they usually won't eat after 6pm.
Meditation is amazing. It's a pain to keep doing, but worth 30min/day. Do the kind of meditation that focuses on breathing. Search for meditation tutorials or "how to meditate".
In order to take a big crap out of your mouth, do breathing exercises.
Breathe in for 4 seconds.
Hold for 4 seconds.
Breathe out 4 seconds.
Hold for 4 seconds before repeating.
Try to do for 5min, several times per day till frequent yawning is just a memory.
Also try finishing showers with cooler water for a couple of minutes. This is said to alkalize the body. Hot water makes body acidic.
Search for "liver chi stagnation" for more info. The Chinese have known about this for 2000 years, so there is some more you could do to help. If you let the yawning go on, what comes next is much worse.
Thanks, I'll check it out. I already do yoga with some breathing stuff but not regularly enough. What do you mean by what comes next is much worse?