Hi Kilsh, headaches are common and are usually the result of dehydration. It is easy to underestimate how much water you need when you are not eating. Drinking more water can make a difference, but a broth style soup can be even better because the salt helps you retain water and replace salts you lose.
Japanese miso soup is my stand by.
Hope you can find a good solution. ⭐️

Hi Kilsh, as Cinque say the most likely cause is not enough water and/or salt. If I get a headache on a FD I always take some salt or have a mug of Bovril. Works every time 🙂