This does potentially sound like migraine, although most migraines are not sharp pain, but definitely pronounced on one side of the head. Over exertion can trigger a migraine episode. I know that mine are usually accompanied by ringing in the ears, however my pain is dull and throbbing rather than sharp or stabbing and is usually accompanied by nausea and sensitivity to light and sound. I do have near daily episodes and have had a migraine that lasted nearly 10 days.
Does he get nauseated with the headache or sensitive to light or sound? These are definitely characteristics of migraine, although everyone is really different with what they experience. What about any visual disturbances?
2-3 headaches per day is a little unusual, but it has happened to me before. I would be more inclined to say that it is most likely the same headache reproducing symptoms multiple times a day, rather than 2 or 3 separate headaches.
I would definitely take him to a good neurologist, try finding one local to you by scouring the websites dedicated to migraine. Read as much as you can and try to see if there are not other symptoms related to the headaches that you are overlooking.
It is possible that it is not a migraine at all, of course. In either case, there is no reason for someone to suffer with that much pain. A good neurologist will be able to identify what kind of headache it is and will likely be able to properly treat it so that your son's quality of life can be greatly improved.
In most cases, when adolescents become afflicted with migraine, they out grow it in time. I realize that doesn't help the immediate problem, but at least it might give you some comfort to know that they will eventually go away, in most cases. Good Luck!