If you have private heatlhcare, just go and see a neurologist, it will be worth it.
Amitriptylline may not work for you, or it may be the wrong dose, either way there are multiple options for migraine prevention.
Next would be make sure you do not have over-use headache - if you take too many triptans they can trigger even more migraines. The golden rule is no more than 2 a week or 6 a month. Any more than that and you can just create even more migraines.
Finally do you know what your triggers are? There are loads of migraine triggers and I didn't realise all of mine until I started really paying attention to them. Some you can't change eg stormy weather, but others you can.
Common ones are being hungry, alcohol, fragrance, not having enough sleep - ideally you should go to bed and get up at the same time every day, blue light from screens, changing the amount of caffeine you have in day.
If you have chronic back pain then physio, a desk assessment if you work at a computer, checking your driving position in the car and the height of your pillow.