Hi J. -
Dont sweat some of the harsh responses you've received. Learn to trust your "mom-sense", it prompted you to write in today.
With that said, at your son's age, if chocolate milk (or even plain milk) is his main source of nutrition, then he is drinking too much of it. He's getting a lot of empty sugar calories which is why he's not eating regular meals. When you cut down on the chocolate milk, he will eat more of the healthy foods you feed him. You may have a bit of a fight on your hands, but be patient and most of all persistent.
My youngest son refused milk at 12 mos old so we moved to transition formula. Since 2, the only milk he will drink is Horizon vanilla milk in a box. He even stopped taking milk in his cereal. To help you compare, I only give my son one box of the vanilla milk maybe 2 or 3 times a week. He gets most of his calcium from other dairy foods like cheese and yogurt, and occasionally ice cream or a Carnation instant breakfast. I also give him a daily calcium gummybear supplement recommended by my doctor.
Here's my suggestion to wean him off of the chocolate milk -
First off, start using less and less chocolate in his milk. He won't know the difference and will quickly become accustomed to it. So, if your at McDonalds and he wants choc milk, buy an extra white milk and mix them in a cup. Secondly, don't make milk his "go to" drink whenever he is thirsty - offer him water or diluted juices some of the time. Lastly, give him milk after his meals rather than before.
I hope that helps you!!
C.