I Am A Diabetic. Why Am I Getting A Constant Headache?
There are no clues in your history to suggest a possible cause - except that it starts in the morning and lasts all day.
There may be refractive error and eyestrain - from looking at the computer
There could be tension - this goes out at night
Sinusitis is also a possibility - lying down allowing to drain.
A constant headache for a fortnight or more needs investigation.
The first thing will be to see an eye doctor - apart from refraction, they will check the eye pressure and also the fundus with ophthalmoscope - papilloedema (swelling on the eye's nerve head) suggests increased pressure on the brain.
If there are no associated symptoms, the next step is to see an Internist or Neurologist. Proper treatment needs proper diagnosis. Proper diagnosis needs tests.
There are specialists exclusively for headache only! There are also special pain management clinics.
In the meantime, you may try NSAID (like ibuprofen. A small dose taken in the night - after supper and one in the morning - after breakfast may help.
Take care
Wishing you speedy recovery
Good luck