Hi fnm my ds2 has epilepsy and I know how scary it is, especially at the start. It was the reason I came on the SN board in the first place and I have found it a great place to stay, especially as ds2 has other behavioural/sensory-related issues which people with NT kids just don't appreciate (not least the incontinence).
Keeping a seizure diary is a good idea because then you have specific answers to the questions all the doctors will ask you. I started off with a separate diary to record his seizures, but then bought myself one of the diaries made by Organised Mum and I use three of the columns just for ds2. (Currently as he's not having seizures I record his energy levels, incontinence and general behaviour.) No-one else will be keeping notes for you - even when ds2 was in hospital the doctors and nurses didn't seem to care that he was having loads of seizures - so they don't really have a measure of how well the medication is working and will go by what you are saying. (That's my experience, anyway.)
I do hope the sodium valproate works for your ds. Liquid is probably better at his age but be aware as he gets older that there are tablet forms too, without the colouring and without artificial sweeteners. My ds2 has done better on these than on the liquid form. I still think it's counter-productve to put colourings known to cause hyperactive behaviour into medicine for children who already have enough going on in their brains.
Anyway ds2 started on sodium valproate (and briefly clobazam as he was still having lots of tonic clonics while the valproate was being ramped up). But he also had lots of myoclonic seizures (we call them his 'little jerks'). Those only went with the addition of lamotrigine, which made him extremely tired when it was being introduced, and had to be ramped up slowly. We were very lucky to be able to control his seizures with the first two drugs we tried. At the moment he's completely weaned off the valproate so he's only on lamotrigine. It was a difficult time when he was still having daily seizures, and once they were under the control there was the worry about what the AEDs were doing to his behaviour and cognitive ability. That's why I have been keen to wean him off the valproate, in particular. But he was seizure free for over 2 years before we started this.
I found the NSE (National Society for Epilepsy) and Epilepsy Action websites were very useful and I still go on the NSE forum from time-to-time. It's not as busy as this one, so if you post a message and only get a few replies, don't think everyone is ignoring you, it might just be that they haven't visited the site for a while.
I remember when ds2 was having regular seizures they really wiped him out, and also he kept complaining of his eyes hurting. One of the most sympathetic people we saw at that time was actually the radiologist doing his EEG, who pointed out that his head was probably hurting a lot after all the seizures, a bit like a bad migraine. So when your son is indicating that his head hurts it might be similar.
I'm glad you have an epilepsy nurse visiting - this provision seems to vary so much around the country and we were never offered anything apart from infrequent appointments with a paediatrician.
Anyway thinking of you, and I have CAT so please feel free to contact me outside of Mumsnet if you want.