Is my lack of energy and low sex drive a possible sign of low testosterone?

Yes, however...: Fatigue and low sex drive are 2 of the most common symptoms of low testosterone, but that is relatively rare (though possible) at age 33 and there are many other potential causes of these symptoms (low thyroid, low adrenal function, depression, heavy metal toxicity etc.). You can easily have this tested to see if it is an issue.