Thank you for your query at DoctorSpring.com.
I understand that you are concerned and will do my best to help you out.
Yawning during periods of inactivity is normal, even when you have been awake for hours.
Only if the yawning is excessive, associated with abnormal daytime sleepiness and poor concentration, it is significant and needs evaluation.
Is any of these present in your case?
Any injury to the rib cannot be related to yawning.
The injury you have had is also nothing to worry about. An injury to the rib is a cause of concern when the ribs are broken or there is difficulty in breathing. I am sure you have not had those. Even if you did, you have made a complete recovery.
So please do not worry about it. If your daily routine is not very engaging, you can add in activities of your interest which are stimulating. This will take care of the yawning.
I hope this was helpful. Feel free to ask queries.