Please be careful and conscious of your symptoms to as glandular fever is one of the most common triggers for Chronic Fatigue Syndrome.
This was me. I actually kept working for 3 months thinking I had just had a bad bout of the flu, and feeling absolutely terrible. I ended up going down in a heap with mild liver damage and Chronic Fatigue Syndrome, which really stuffed up the next few years.
Not sure if you can stomach it, but maybe something like Sustagen might stop you from losing too much weight? At my worst I was living on Sustagen, Just Right bars, peanut butter and English muffins with vegemite....not a diet I'd recommend, though, as I dropped 17 kgs and felt like crap.
Apart from that I'd say eat pretty simple unprocessed foods, not too much animal fats (from meat or dairy), no alcohol, lots of water.
Mainly, though, just rest. Doesn't have to be sleep, but just don't move around too much if it's at all possible.