If you have a few days to try this, keep track of your wake up times to see if you come closer to your built-in alarm clock's setting. You could even graph how far off you were from the time you wanted to wake up by graphing number of minutes away from your built-in alarm clock's setting. See if there are any patterns to your graph. No one really knows the cause and purpose of yawning. However, yawns do appear to follow a daily cycle.
Yawns seem to occur most often soon after waking and about an about before bedtime.
See if your yawning behavior has a similar cycle. Keep track of the number of your yawns and the time that they occur from the time you wake up to the time you go to sleep. Print out this YAWN worksheet to record your yawns. The most difficult part of this experiment is remembering to record every one of your yawns, so keep the worksheet is a handy place. Add up the number of yawns that occurred in each half hour period and plot them out on a graph.