Headache often means too much nic. How much are you
vaping? You can over-nic yourself on any level of nic if you vape a lot. I over-nicced myself once on 12mg when I was normally vaping 18mg just because I vaped that 12mg Peach way too much without stopping.
You could try some 12mg at times when you vape a lot. 3 drags of 12mg = 2 drags of 18mg.
And drink fluids too, but headache when vaping a lot almost certainly is over-nicced headache. One other possibility is if a person uses auto batteries some will get a headache from dragging hard a lot, or if a person has TMJ a combination of the dragging and the large mouthpiece can trigger their jaw-related headaches.