It could be a neurological problem. It's less likely, but Those symptoms could also be caused by Borrelia? Do you have Borrelia where you live?
Any child of 12 who is experiencing such pain and discomfort should be seen by a doctor. Self medication is not always the right thing to do....I would have had him checked out personally.
take him to the doctor, it could be an allergic reaction
Did the pains appear after he took the meds or before he did and how long before ?