Ok, if you're sure she's checking nutritional levels and not just pulling liver panels or something (sorry, I'm not a medical doctor) then no worry!

You can eat foods that make you hungry.
I know back in "the days" they gave the elderly at the nursing homes Ovaltine because it made them hungry and they ate.

I would go the nutrition shakes or sports protein drinks or bars. Watch out for too much sugar though, as that would be counterproductive I think.

Maybe you need to bulk your muscles up a bit through exercise/weight bearing? That would add weight, and appearance, and would allow you to eat even more!