Hi IF, only just noticed your message - sorry away withthe fairies this week packing labour bags and building cots!
What I experience doesn't sound like what's happening to you though that doesn't rule it out I'm afraid, it's a difficult one for doctors to diagnose. Migraines tend to be, but not always, restricted to one side of the head/body (which sounds like it shoud be better but it just means yu've got a 'normal' side to compare the pain against). I have classic migraine which means I get 'aura' but 80-85% of people with migraine don't have aura. An aura can be seeing lights, blurred vision, hearing noise, feeling deaf, numbness or paralysis etc etc - anything neurological - it's thought to be caused by the initial restriction of blood flow to the brain that happens during an attack. You also have a definite 'beginning' to each episode. Chronic migraine is when you (unmedicated) have a migraine for more than 50% of the time. It's slightly different pain-wise as it becomes more bearable the longer the attack goes on but there's some debate as to whether that's becasue the pain decreases or your tolerance increases as you get used to the pain. Chronic migraine often happens because the initial migraines weren't treated properly and the wrong medication is given and the migraines then become intermingled with medication over-use headaches. They can also happen because there isn't long enough between attacks to recover properly, like getting a bruise and then something else hits you on the same spot, you don't recover as quick, so the next one lasts longer andyou're more susceptible to aother attack- bit of a downward spiral - this process isn't restricted to migraine though so might be relevant to you.
Sorry, I could go on for ages - it's the problem with headache really, there arelots of causes and different types. There is a really good site though that goes through the classification of headaches - see here - go to publications and click on the download in separate sections link. The reassuring thing I can tell you is that when there's something very serious underlying a headache it tends to intensify over time and never get better and that doesn't sound like what's happening to you.
The problem you have now is that you've had it for so long, it might be complicated by the medication you're taking (see here ). If you can, try and think back to what the original headache felt like and ask yourself if it's changed at all. If it has you need to go off your original symptoms to try and work out what's going on.
Could continue the essay (sorry about that) but I'll let you digest the info in the links first - feel free to ask any more questions or for more info on any of the kinds of headache mentioned. Hope you're ok and manaing the waiting - week to go so you're halfway there.