I have not used Levemir but as you have increased the dose, I wonder if you are experiencing hypos which definitely give me headaches.
Are you using a CGM or Libre which could highlight these whilst sleeping?
I have been using Levimir for a few years now and cannot say that I noticed any increase in headaches when I swapped over from Abasaglar. But we're all different so it may be affecting you in way that did not affect me.