Ian, I am 40 years old but my epilepsy also started when my hormones kicked in. Stress and epilepsy are known to be linked (at least I have read numerous books which mention this link) so the reaction of the neurologists surprises me.
However, progesterone is a known anti convulsant and Estrogen a known trigger for epilepsy. Proof of this was when I was pregnant I gave up my AEDs- progesterone as you know rises through the roof when you are pregnant-no seizures. My consultant was absolutely furious. Actually I managed to keep of AEDs for 10 years but as I've grown older I think my progesterone has naturally lowered and my epilepsy has returned. I currently take 500mg valporate a day which is a very low dose, but I do have an occasional seizure around my menstrual cycle which I am trying to control now through various means-to soon to measure success yet. But probably magnesium salts won't be the only supplement that you need.
As mine happens on waking I am now experimenting with a variety of things (magnesium sulphate, taurine, B complex and breathing exercises
https://www.youtube.com/watch?v=JhK549uGvhc buteyko-watch here if you're interested.) I have also read the vitamin D can be helpful.
Don't let neurologists put you off. Often epilepsy isn't their specialty and they may not be interested in this area. I stopped going to neurologists to be honest because so many of them were just not interested in you as a person, and some have such blinkered perceptions it really put me off. Anyway, you may have to try several. I did go on he progesterone coil which controlled my seizures for a time, and then they broke through again, although this is not always healthy method of control either.
Oh the cannabis! I'm not with it today. No, personally I haven't tried it. It might be worth trying but it might have an detrimental effect on your memory. I would try the breathing first-it's free and it's relaxing. I'm going to see if the breathing works first. Personally I would save up your money for biofeedback