C.F.
I would also go to a children's ER, say at St. Joe's or UCH, depending on where you're at. If nothing else, they'll do bloodwork to rule things, such as cancer, out. If he has high levels of anything that could cause it, then it'll show up in the bloodwork, too. Plus, you can still keep the appointment with the specialist, and take with you all the testing that was already done at the ER. It'll save you a step. You know the specialist will want to do an MRI or bloodwork anyway, and you'll probably have another week or two after the visit for a follow-up appointment where the specialist will review the results. There are a lot of things it could be, as others below mentioned. Could be an eye infection (though that would be noticeable), could be sinus pain (there are sinus ducts behind the eyes), a migraine (you could try getting sugar out of his diet for a while, and increasing fluids), an undiagnosed eye disease, or it could be something scary-- cancer of the eye, or tumor behind the eye, etc. etc. Once or two a day over a period weeks is something I would definitely want taken seriously. Sometimes primaries DON'T take things seriously, sadly enough. Better to over-react then to ignore a possibly bad situation.