Not sure if it's been asked but when you went to the GP, did they check your blood pressure?
I have been a migraine sufferer since my teenage hormones hit but about 2 years ago I found I had some form of headache almost every day along with things such as a twitch in my eye, pressure at the top of my nose, dizzy spells and some nosebleeds.
Lots of diary keeping and tests later, it turned out I had dangerously high blood pressure. Took 7 weeks off work while they got it down and found a medication that suits me and it's been mostly fine since (well, back to my standard migraines anyway).
Try not to take too many vitamins / supplements all in one go as you won't know which one is having what effect.
Don't take painkillers everyday as they can actually end up causing headaches.
If you are going to take medication, take the right one. Paracetamol isn't always best (I take aspirin for the start of a migraine for example).
Make sure you're not dehydrated, preferably with water. I saw you said you drink fizzy drinks - due to the sugar tax, some fizzy drinks have altered their recipes so the sweeteners are different and some have been linked to all sorts (read up on aspartame).
When you keep your diary, don't forget to note what you eat / drink and when, how much sleep you get, any medications you take and how you feel, including the type of pain you feel and score it out of 10.
I found triggers for my migraines are as random as having more than 8 hours sleep and the smell of raw onion, and pain relievers as random as putting my feet in hot water and using a menthol vicks inhaler.