Hi M.,
I would agree that the place to start is a definitive diagnosis from your son's doctor. Headaches can mean a lot of different things. That said...
My mother gets migraines something fierce, generally brought on by stress or just after a major stressful event passes. (Losing your cat would qualify as a major stressor, especially for a 7-y-o.) I wish there was something i could do for my mother, but I think she has multiple contributing factors, including gluten intolerance which she ignores, and a very fragile neurosystem.
I got migraines in my youth, and haven't had one since my late teens. When I was a teenager I also suffered from back pain and depression. When I still lived at home I got some relief from biofeedback, which teaches the user some control over physiologic processes. We can never live completely stress free lives, but there are ways we can learn to cope better. I also do yoga religiously, and that helps enormously. Migraines can also often correlate with food intolerances, I think gluten and shellfish allergies are common migraine causers. Gluten is in so much, it's a tough one to get out of your diet.
Since you suffer from them too, it sounds like there could be a congenital issue at work here. You can get tested for gluten intolerance, and I would recommend it because the list of potential complications is long and they are severe. My mother has night-time epilepsy, thyroid problems, anemia, chronic fatigue and fibromyalgia, migraine, chronic depression, ack! the list goes on. She refuses to examine the cause though. One out of a hundred people are gluten intolerant, it's really common. We don't hear about it much in this country because the wheat lobby is huge and we love our food additives.
Good luck to you and your son.