@Eviolle thank you for your kind reply, and I am so sorry you're going through this at the same time as being mum to a LO.
There's some research out there that these cysts can grow during hormonal surges (with the greatest respect I doubt your GP has done as much reading as some of us!), and the "99% don't grow" is literally a number plucked from thin air as how many people have CT or MRI scans before there's an issue...
Medication which did reduce the frequency and intensity of the headaches, and non-epileptic seizures was lamotrigine (which I believe they also sometimes give for migraines). It did make him a bit zombified but he definitely preferred that to the pain. It might be worth asking to try that as a short term fix?
Ultimately though you really need ICP monitoring. The skull is a closed box, if you suddenly inflate a "water balloon" inside then everything else gets squished - it's not rocket science, but I am honestly amazed that I was on the verge of having to get visual aids to explain this to some trained doctors!
However, just to keep subscribers to the NHS mantra happy, it could be: a vitamin deficiency, hormone imbalance, not enough water, too much water, too much screen time, too much sleep, not enough sleep, not enjoying school (motherhood?), eating without drinking, drinking too much whilst eating, your sinuses (epic story on that one!) or you could just be making the whole thing up for attention.
Please, please get someone to advocate for you. Next appointment they should go with you and say they're taking notes. Have a list of questions (happy to PM these to you). You're feeling rubbish and you're stressed and not being listened to, so that makes it hard to get your entirely rational point of view across.