Just reading and wondering how you are doing today. Perhaps by writing down each time you (all) eat something, will not only help you show doctor how you are trying and eating, but yourself too, and if you aren't eating enough, will show you that, too.
Depression and stress make it near impossible to reply to sudden, unexpected questions. Try and memorize by rote some simple answers. If you get really stuck and caught off guard (for any reason) try a clever smirk, twist of the head, raise of the eyebrow, or a wink to make it seem that you are choosing not to answer. (Well, you are!) Or, ignore the question and reply back with one about them... redirecting their focus.
After I was first injured (well, a for a few years) I had trouble responding to someone asking my name. My brain felt so scrambled, I, too, felt the "How am I supposed to answer that??" I learned that just because someone asks a question, I am not required to come up with a reply. Give yourself that permission, too.

TC