I get hot and sour soup from chinese takeouts. I know it's not the lowest carb option as I'm sure the corn starch it some, but it beats many other options, and it opens my head up if it's more hot than sour.
Another of my faves is chicken meat, chicken broth, salt, ginger (fresh or not depending on the pantry), veggies - usually in shreds or small dice, egg scrambled and poured in when nearly done then add some lemon juice. Sort of egg drop soup? I'm no good at egg ribbons, but it still tastes good. As far as measurements - I'm no good at measuring or being consistent, just keep it more broth than stuff, and go a little salty.
Taco soup - I don't recall my exact recipe - but it involves cheese, rotel tomatoes or plain diced tomatoes, ground beef, taco seasoning. I'd make it spicy if my sinuses were clogged.
good stash of teas, low carb hot cocoa, coffee should all be good too.
Sorry you are getting sick. I've started a scratchy throat so I'm afraid I am too. Feel fine in morning, by the time I'm leaving work my throats scratchy.
Oh, dear.
Get well soon!!!