Hi Suzpar and welcome to the forum
I too am a fellow sufferer. I have headaches every day for a good 30 yrs, and also migraines most weeks. I am in my 10th week of fasting. To begin with my headaches slightly improved, but then settled back to how they were.
Now some fast days I am suffering more. I am on medication for the migraines. Like you are finding with the timing, mid afternoon can be a killer for a migraine to appear with reduced food
I am determined not to give in and say, oh its the diet, easy to do as we are knew to this way of eating. I try to work through the headaches.
Your body will also take a few weeks to adjust, so (excuse the pun), some pain now will hopefully be worth it when you stand on the scales
I find they do vary in intensity through the day, and I can put this down to the food on fasting. I was drinking lots of water to keep hunger at bay, prob in excess of 3 litres (I don't drink tea or coffee). I have tried to cut this back incase I am flushing minerals and salt out of my system. My headaches were more acute with the volume of water I was drinking.
I think I cut back a little too much, so have eased myself gently back into water.
Maybe keep a record of when they come on, intensity, what have you eaten/drunk etc. It could be our bodies are crying out for something as simple as salt, or a drink.
I have lost 15lbs in 9 weeks, so the motivation to keep going is high ! If I get a migraine on a fast day, I eat the reduced and go to bed early. Having a bad headache next day after a fast is something I experience sometimes, but cannot say 100% if I would be any different without fasting.
I feel for you, knowing exactly what its like
Good luck and lots of positive thinking for less headaches !
Gill
p.s. Not sure if any of this helps !