Brief Answer:
Headache lasting 5-6 days is worrisome, could be sinusitis.

Detailed Answer:
Hello Mr XXXXXXX

Thank you for posting your question here on healthcaremagic.com

First off, there are quite a lot of reasons for headache, and a persistent one as described by you does indeed warrant looking into it seriously.

The common causes for headache include,
1.     Problems with the eyes, such as
a.     Refractive errors (far or near sightedness),
b.     Strain and eye fatigue
c.     Dry eyes
d.     Increased pressure inside the eye (glaucoma),
e.     Optic nerve problems/retinal problems.
2.     Problems with the nose and ears
a.     Sinusitis
b.     Common cold
c.     Ear infection
3.     Problems with the arteries or nerves
a.     Vascular headache (migraine)
b.     Trigeminal neuralgia
c.     Temporal arteritis
4.     Problems with the teeth like
a.     Dental caries
b.     Dental abscess etc.
5.     Problems with brain and intracranial pathology like
a.     Infection of the coverings of the brain (meningitis)
b.     Intracranial tumours
c.     Raised intracranial pressure due to oedema (swelling of the brain)
d.     Metabolic encephalopathies (hypo/hypernatremia etc.)
This list is not exhaustive, so it is not possible to tell you the cause without a thorough clinical examination and appropriate investigations.

My suggestion to you at this point is, consult a physician first (MD general medicine), and get yourself looked at to rule out the causes.
You will most likely be asked to get a few blood tests like CBC, Blood urea, serum creatinine, and serum electrolytes, urine routine exam and possibly an X-ray of the paranasal sinuses done to rule out the causes one by one.

For the time being however, you can take paracetamol 650 mg (Dolo 650), tablets thrice a day till you meet the doctor.
Be sure to explain the headache clearly and also explain all the other symptoms you may be suffering from to the doctor so that the examining doctor gets a clear picture of what is going on.

I suppose this is sufficient for you at this time, if you have any doubts and further questions, I would be glad to answer them.

Wishing you speedy recovery and best of health.

Best regards.

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