Because the thing is, they never happened that frequently. Maybe once every few weeks. I was under the vague soap opera impression that tumours in your head gave you headaches continously, but apparently this is not necessarily the case! After my operation, I had headaches more frequently for a month or two (not particularly surprising given that surgeons had been rummaging around in there with sharpened implements), maybe a couple of times a week.**
My pituitary adenoma headaches are actually usually pretty similar. Previously, I would get pain all around the edge of my right eye socket, and right at the back of my eye - and it is somewhat disconcerting to feel where your eyeball must be - although since the surgery, it has improved (yay!) - I only really get it in the upper left-hand corner of my eye, which is where the pain used to be worst. I always feel slightly better if I massage that corner of my eyebrow; this has now turned into a habit which I catch myself doing even when my head is not hurting.
But ladies and gents of the internet - fret not if your headache sounds similar, for you probably do not have a tumour in your head (though that does not mean that your headache could not be seriously unfortunate). The Power of The Internet informs me that there are all sorts of different types of headaches even amongst pituitary tumour patients, so pfft, who knows. Just go hassle your doctor about it.
* Paracetemol makes me cough. Apparently this is odd.
** I wasn't allowed to take ibuprofen due to being on steroids, and I wasn't supposed to cough lots, which ruled out paracetemol. This put me in something of a quandry for painkillers, but as