Congrats on your certification!
Cenotes are amazing. It's good that you are aware that it's overhead and there are significantly more risks associated with diving this enviroment that in open water. Definitely not a place to be cavalier.
However, if you have good buoyancy control and are comfortable in the water, then the guided cenote dive can be a dazzling experience. On the other hand, if you are still figuring things out, then you should not go into the cenotes. The cenotes will be there for your next trip back to mexico.
Personally, it took me till around dive #20 to get comfortable in the water and have some situational awareness. Of course, everyone progresses at their own rate, but be honest about your skills.
There are some good threads on this topic the past couple of months:
* Cenotes for OW?
http://www.scubaboard.com/showthread.php?t=130471
*cenotes experience/certification?
http://www.scubaboard.com/showthread.php?t=122678
From Dennis' post (#23) in the above thread
http://www.scubaboard.com/showpost.php?p=1425126&postcount=23
you can read the safety guidelines used, and what Dennis does to make sure that people are safe, comfortable, and having a good time.
If you are going to be in Akumal for many days of diving, I would do a guided cenote dive later on your vacation. While on the reef dives, take the time to work on your buoyancy, trim, and overall comfort in the water. Get a critique from the dive master too, and see where you are at.
Have a great time.