My Son's Eating Problem

I noticed my son is not been eating so good lately. I just hate to tell you this but sometimes he makes my patience ran out of keep telling him that he must eat. Just like earlier tonight, i have to spank him just to make him eat but in the end he just threw up because he's been crying so hard. I am really upset why he is not eating like he used to anymore. I am getting so worried that he's just keep depending on milk. I told him that he can't have milk tonight or tomorrow or so. He has to eat solid food and he should follow mommy because i am telling what he must learn. He needs to eat enable for him to gain energy. Mommy will give him time out this time from drinking milk in the bottle. It's hard for me to do this but i have to for him to learn. I am worried for my son, i love him of course that's why i am like a crazy mom now thinking what's the best thing to do to make him eat regular food. I guess i'll buy him some vitamins so he will regain his appetite that he used to have.