weaning off meds?

Hi,
I'm trying to wean myself off of my migraine prevention meds, mostly becuz they are not "preventing". I've been on Elavil (25mgs) for about 3 years and Neurontin (300mgs)for about 9 months. I know the doses are low, but my system is very sensitive and I could not increase the doses. I've weaned myself to 150mg of Neurontin, I did that on the 11th of this month. I tried to stop the Elavil, but I wake up at 0130 and can't get back to sleep. I tried to use Melatonin instead, but it gave me a migrine. The only thing these meds have done for me is helped me gain weight (yuck).
How long should I stay on the 150mg and when can I drop to 75mg? I don't want to freak my system out by stopping to soon?
Thanks,
Beth