Being sick sucks. I had mono last fall, and I can tell you I seriously ate like nothing while I was sick. For breakfast I'd have about three bites of oatmeal, for lunch three spoonfuls of soup, and for dinner three bites of whatever we were eating (which was hopefully soft and mushy), if even that much. I definitely lost weight while I was sick, but as soon as I got better I was RAVENOUS and I ate a huge amount which made up for it!
It's okay though, my body needed to make up for the deficit, since mono lasts so long (I was sick about 5-6 weeks).
I hope you feel better soon! Don't push yourself too hard if you're feeling crappy!