I think it rather depends on what type of headache it is.
Migraines and headaches are very different, and then headaches come as tension headaches, and eye strain and... goodness, all sorts of different ones.
I did read once that most headaches are dehydration, and that the glass of water you take the pain killer with actually does more to help it than the tablet. Which makes a kind of sense - especially with the amount of extra fluid we need on LCHF.
So I suppose as a shortlist
- have a few glasses of water, and see if it goes
- up your minerals, as
@Robbity suggests (cup of bovril or broth is a good starter)
- review posture, hours at screen, position of chair...
- need eye test?
- sinus? hayfever? etc
and if none of those help, trundle to doc without delay.
Hope that helps.