Hi,
What other symptoms do you have?
Does the pain vary in intensity during the day?
What all tests have you undergone?
The reasons for constant headache are many like sinusitis, allergy headache, tension, hypoglycaemia, dehydration, high blood pressure, ear infections. The possibilities are many. Did you undergo CT scan or MRI of the brain?
Please elaborate your symptoms and then maybe i will be able to help you more.
I generally suffer from migraines, but once I couldn´t get rid of a stubborn headache for a week. I used my typical medication and it did nothing for me. After visiting with a dentist he discovered I had an infection which was provoking my terrible headaches (btw no toothache). After an antibiotic, the headaches ceased. i would advise to check with a neuro just to be sure. Good luck.