my son wont eat

Hi. So my son is almost five he will be starting school this fall. We have been having a problem with his eating habbits for over a year now. He will go days with out eating and he wont eat meat or veggies. Only starchy foods and milk. It is very hard and you can see his bones he is sooo skinny and his tummy is starting to extand out more and more. I keep getting told he will grow out of it but i dont beleive he will i need some help please