I'm new to this forum but very old as far as chronic daily migraine is concerned. Mine began same age as yours and became daily by age 18. This is my first post and I'm not up to writing much now but was concerned you'd had no replies, so far, and I wanted to say don't give up, don't accept everything the doctors tell you without getting well-informed second or third opinions.
One thing you may consider is the perennial question of whether you have rebound pain from regular pain meds, I have been told any sort, even triptans, can cause this. In my case staying off pain meds completely - had to be put in semi-coma to endure it - made no difference, the headaches and migraines continued.
If you are depressed I empathise with the zombie response to nortryptiline; I have tried every preventive, many to extremely high dosages which left me incapable of basic functions. Point to consider is you may not have yet tried SSRIs, anti-depressants which affect levels of serotonin in the brain. 5HTP is a natural supplement which acts in the same way but has not been tested for appropriate dosage. I am currently trialling Sertraline having found the 5HTP a bit weird.
I haven't tried SSRI's yet, however, I don't think they will do much good to prevent my migraines. I do wonder a bit about
the potential for me to use it as an anti-depressant though. Nortriptyline is supposed to work just as well and might even better than SSRI's so... I see it as my only reasonable option now is to try topiramate and see if that can prevent my migraines like depakote did or maybe even better. The reason I opted to use Nortriptyline instead of Topiramate is because I don't want to feel dumb as a rock, like I did on Depakote. That is my main fear. I have always considered myself very intelligent, but now as the school work keeps on piling up, I doubt it. I remember my neurologist told me 6 years ago that people with migraines are smarter than people without, but I know that recent studies have busted that myth.
And on the subject of rebound headaches from triptans or pain killers, I discontinued use of triptans and pain killers this summer and did not find it to lessen the frequency and intensity of my migraines. I have spoken with my neurologist and he doubted I had Medication Overuse Headache.