What to eat when u r sick in Japan?

A friend of mine went through the same thing and he has great recommendations:
-Soba (cold)
-Kakigouri (the shaved ice, it numbs the pain and feels good)
-7-11 frozen deserts from the freezer (they're pretty pimping).
-Cold soba is probably the best bet

 Also, even though hot food may hurt your throat, a very healty and delicious dish in Japan is the Nabe:
https://planetyze.com/en/japan/nara/asuka-nabe-hot-pot
Here are some more nabe pictures so you can understand what is is: https://goo.gl/Tf3825
There are great nabe restaurants, you can search for that.

If you are looking for the cold soba or udon options, there is this great chain called Nakau that you can find everywhere: https://www.nakau.co.jp/en

I hope this helps and that you get better soon! =)
Enjoy yout trip!