Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with your doctor.
Without the ability to examine your son and obtain a history, I can not tell you what the exact cause of your symptoms is. However I will try to provide you with some useful information.
In adolescents, migraines are common, and in children with a strong family history, migraines can occur at this age and be severe. I am not sure what you mean by the statement the headache has not subsided. If it is occuring frequently, but there are headache-free days on some days, this could just be severe, frequent migraine, in which case some preventative migraine therapies are indicated.
However, if the headache is literally occuring daily, continuously, without relief, there are several possibilities. One of the most common scenarios is what is termed transformed migraine. This includes medication rebound or medication overuse headache: medications as simple as tylenol or advil if used too much can cause rebound headaches that are even worse then the headaches for which the medications were started for. This is very common and is most likely to occur with use of any medication headache more than a few times a week. It can occur with all the commonly used headache medications such as ibuprofen, triptans (such as imitrex), fioricet, and commonly with any type of narcotic such as tylenol #3, dilaudid, percocet, etc. The treatment is difficult, but basically involves weaning off the offending agent and replacing it with another that is later weaned off, combined with a more long-term solution. This should be done under strict guidance by a specialist, preferably a headache specialist, or else the headache will not improve and withdrawal side effects can occur.
Another possibility is that the headache is not a primary headache disorder (not a migraine) but rather a secondary headache disorder. Headaches can be divided into primary and secondary. Primary headache disorders are headaches without a direct cause. These are diagnosed after secondary causes have been excluded. Secondary headache disorders are due to an underlying problem, there are many many causes but some include medication side effects, systemic illness, nervous system infection, tumors, bleeds in the brain or clots in the veins of the brain, and others, such as due to infection, elevated pressures around the brain, tumors etc. It sounds you have been told there is not elevated pressure in the brain; this may have been based on eye examination, and this is reassuring. It also sounds like you are on the right track with a plan for an MRI; a normal MRI does exclude several secondary causes of headache, including tumors, vascular malformations, and others but there are some secondary headache causes not excluded by imaging. If there is continued concern about specific types of secondary headache after the MRI is done, further testing such as lumbar puncture may be indicated.
Continued follow up with your son's neurologist is recommended, with evaluation by a pediatric neurologist and/or a headache specialist (a neurologist specialized in headache medicine) as indicated.
Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck.
This is not to concern you, however this is too encourage you that you are on the right track adn that you should push for your son in finding anwers.
One thing I notice you said he gets them after he eats. Now migranes can have food tiggers, if this is happening, it can be the cause of your son's serious migranes. Watch his diet carefully. As a mother I understand how difficult it is when our kids are sick and we cannot find what is wrong. Try not to give your son too many diffrent meds for the headaches it cause referred headaches as well. I am thinking of you and your son. Mya daughter is 13 now and on supervered meds for the headaches adn her seizure activity she stated to have. I hope all is well with the MRI....Blessing.
Take care.