Electrolytes with plenty of water should help with a headache. Water, tea, coffee during your fasting window, and that can of soda with one of the meals. Between meals, water, tea, and coffee only will be best.Try wider eating window and 3 meals or 2 meals + 1 snack. For me, the first week was the worst, the second so-so and then so much easier. Good luck!
How many calories did you eat yesterday?
You don’t need to switch to a shorter schedule but you need to make sure you’re eating the right amount of good food (ie not empty carbs - protein, fibre, vitamins) in your eating window to see you through the fasting periods.
Break today if you have a headache or drink some water with salt (little bit) and see if that helps. Just try again tomorrow if you need to break the fast. It’s about starting a long term healthy habit, not charging forward for the sake of hitting a timer, so look out for yourself.
When I started IF I would panic eat at the very last minute. I felt grumpy and would get sudden hunger pangs that would just as quickly recede. It passes.
Water with a bit of salt in it can help. I liked to focus on how when I was fasting that I was succeeding, that I was doing it. That all I needed to do to succeed was not eat right now. I didn’t need to avoid a food, or count my calories. I needed to not eat, and that was the success. After 2-3 weeks it turned into my new normal and I love it.