Definatly get some testing done,the hunger he has may be part of the problem , if you wish to refer to a pediatrician we have an expert/ doctor forum put your question in there .good luck
I know you asked this question to the pediatric endocrinologist, but I just wanted to encourage you to proceed with consultation with the endocrinologist. In my opinion, your pediatrician made a terrible mistake in not having referred him sooner. If you plot your son on the CDC growth charts at 2 and 3, it will give you an idea as to just how far above the average he is. Even *IF* there is not anything medically going on that is causing this, he is at great risk for future health problems. But my hunch is that there is something going on, so as scary as it is, it is something you have to look into as his parent. Good luck (((HUGS)))
Take him in for testing, for sure. If all is well, you will have that question off your mind, and if not, you are in a better position to do what needs to be done early enough to have a good impact. For the record, my 4-year-old weighs 38 lbs. He is just slightly taller than the norm for his age, but not by much, and the 38 lbs. is considered to be only very slightly underweight for his age.