Before coming to Scotland, I had all my medical tests done, had my eyes tested, and had necessary dental work done. Unfortunately, one of the inlays I got doesn't seem to be working out, and I'm experiencing a lot of sensitivity to temperature and food.
When I went to the dentist, the receptionist set up an appointment for me and said she'd extended it because I had toothache. Have toothache? I thought.
Later that same day I visited the blood donor clinic just down the road from the university. I had intended to give blood, but the nurse who interviewed me told me that I couldn't because I had toothache. That did it. I appears that here in Scotland at least, toothache can be a non-count noun. A quick query of the BNC suggests that it can be either count or non-count, but non-count instances dominate.
"That's weird," I thought. In Canada, one has a toothache (though one wishes one didn't). It's always countable, just like headache and the The Strathy corpus of Canadian English includes not a single instance of HAVE + toothache. Sure enough, even in the UK one has countable headaches (though at times, no doubt, they can appear uncountable), and it doesn't appear as a non-count noun. But then I started to wonder about other aches. It looks like count and non-count stomach ache are in competition here in the UK, while in Canada, it too is strictly countable.
Heartache, though, is overwhelmingly non-count on both sides of Atlantic, even though you do get instances of a heartache, as attested by this song.