Increase your salt intake! It helped me so much!! Look up “Keto adaptive” or “keto flu”, it is a very real thing. Your body is adjusting and detoxing. Increased water intake and salt intake were my saving graces.
You’re not getting enough electrolytes. Your body is struggling to keep itself hydrated and it’s resulting in headaches. What kind of fasting schedule are you on? Look into “snake juice” and try drinking it during your fasting periods.