Share 'Picky Eater...HELP'

So my son has decided that he will not eat ANYTHING except bananas, rice, carrots, green beans and peas. He REFUSES to touch or even taste anything. I have tried to "hide" foods in everything trying to get him to just taste it, to no avail. I am at my wits end. My husband says when he gets hungry he will eat it, but he doesnt he just screams and cries until he makes himself sick. He is allergic...