Mr.D,
The title 'my grains drive me insane' could be about a number of things really but in my opinion this is about things from the past or possibly present getting on your nerves and driving you more insane than you already were, now I can comment on this as I'm insane too hehe

Bang, Bang, Bang!
Jack hammers my pounding skull
from the brain side out
^
I love the description here it seems to me your talking about a migraine as they're awful things though I think this goes further than that maybe it's about the untrue thoughts are banging from the inside of your mind and are trying to get out so I suggest you let them.

Slam, Slam, Slam
a rusty spanner splinters
my cry eye socket
^
Ouch, that's gotta hurt but I'm guessing this is about hay-fever because it's so scratchy and itchy and would feel as though splinters are in your eye although I've got dry eye and it feels pretty much the same and despite the name my eyes water alot. Again, wonderful description.

Drip, Drip, Drip
congealed corneas droops their gloop
face side down... so down
^
A harsh reality, makes me think of headache auras and how people who suffer migraines can sometimes get signs (can't think of the real word) that they're going to get a headache which is good for them but gutting for those of us who suffer daily and don't haha I like the repetition of the word down and it shows how debilitating

Head Crushing
carnage needs more than just two
Paracetamol
^
Ahh now this makes me believe this was actually about a migraine, these types of headaches are awful although my pressure headaches are much, much worse for me as it feels like my head is in a vice due to my IIH.

All in all a brilliant piece. I love the repetition of the words, it makes it feel more real, in my opinion.
Take care and stay safe,
Em xx