I know, Leonie. It's a very particular sort of headache too, isn't it? Feels like your head has been squashed in a vice whilst simultaneously being burnt from the inside out...
I feel bad saying that since they jumped my dose up, aside from the side effects of getting even lardier, I'm now nearly 13 stone when my usual weight is just over 10, I feel better than I have in ages. 
If it wasn't for the residual pain in my foof, I'd be painting my front room!!
I do think it IS a massive case of trial and error when it comes to finding the right AED at the right dose for each individual with epilepsy.
MyGranny has been fine on Tegretol for decades, and is 98% seizure free unless under severe stress or driving at normal speed over a particular bridge...
Yet Tegretol made my liver start to fail.
Gabapentin seems to work ok for me, until my body gets used to each dose except for the week before my period.
I think you WILL find an AED that helps, but it may take a while - I was dxd in 2003, and it wasn't until 2008 that we hit upon the Gabapentin for me. So it took 5 years.
And then I had a med break for 2.5 years from 2009-2011. Went back on the Gabapentin, and dose rises each time szs break through.
It just takes time - each person has their own body chemistry, and so different AED's work better for different people.
I know of 3 people on Keppra - 2 get the rages, 1 doesn't...
Are you getting enough sleep?
I always find that lack of sleep is a MASSIVE trigger. You do NEED to be aiming for 8 hrs a night. Every night. I don't manage it, some nights I'm lucky to get 2 hrs, but that's down to DS3!