Have you been to your GP, i'd discuss this and any other 'symptoms' you have, i get quite severe headaches due to eye strain even though i wear glasses constantly.
I also get them if i have not had enough water (my biggest issue when i was PG) or have been in the sun too long.
Lots of things can cause headaches but if it's gone this long i would have a chat with your GP.
Hope it's gone ASAP.