First off, how much milk does he drink throughout the day. Talk to your pediatrician.....only give him a container like you would buy say for lunch from Kwik Trip throughout the day otherwise water. Do not feed the junk, whether sweet snacks or fruit snacks, i.e., give him what he needs and that is it. It will take a day or two, BUT he will get hungry and he will eat.....try a few thinks that he might like or has liked and just make it balanced and maybe give a little more as he gets a bigger appetite. When he eats do not give him his milk or drink until he has eaten some and again this works better once you stop feeding all snacks, etc.
Have had to deal with this myself, he would only eat oatmeal or have so much milk throughout the day that he was full or almost full most of the time.....so know where you are coming from. Hope this helps