Brief Answer:
Read below

Detailed Answer:
I read your question carefully and I understand your concern about your little son.

While not as common as in adults headache is a problem often encountered in children as well. They can be divided in primary and secondary headaches.

Secondary headaches mean that there is an identifiable cause, while primary headaches are the ones for which no identifiable cause is found, headaches like migraine and tension type headache. Given the duration of the headache tension type headache seems to be more probable in your son's case (although you should provide some more info on location of pain, character, accompanying symptoms such as nausea, vomiting, increased sensitivity to light and noise etc)

So you should understand that there is not necessarily a cause to be found in all headache patients. The duty of the physician is to distinguish these primary headaches without a cause from those with a cause such as a tumor, stroke, infection etc. In your case your doctors seem to have done that as he has done the best test for that purpose, a MRI which would detect such causes. So you should feel relieved that no cause is found on MRI really, as usually it is a question of threatening or disabling conditions.

Once a secondary headache has been excluded then primary headache should be treated. It involves treatment of the attacks which usually is through over the counter pain killers such as Ibuprofen and when pain is frequent, medication to prevent the headache episodes (lower the frequency at least). Preventive treatment may include beta blockers like propranolol, anticonvulsants like valproic acid, or antidepressants like amitriptyline.

It is also important to keep a headache diary (can find models online) in order to identify possible triggering factors like types of food or physical exertion.

I remain at your disposal for other questions.

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