Sorry to hear you arent feeling so well, dont worry too much about your bg levels at the moment, your body is fighting an illness.
Try to eat something light, something low carb, eg chicken soup would be good, you can liquidise soups and sip.
Have plenty of hot drinks, herbal or fruit teas, cocoa made with cream or coconut milk.
Multivitamin/B Vit has been mentioned, but best supplement by far is elderberry extract, its sold under Sambucol, and I would urge anyone to collect fresh elderberries when they are in season, freeze and eat stewed with a little sweetener and cinnamon, they are lovely with home made vanilla ice cream or yoghurt.
Elderberries really do seem to boost the immune system, my family have used them for years and they truly do shorten the duration of a cold/flu.
Hope you feel better soon x