Welcome To BYC
Are you chicks showing symptoms of Coccidiosis?
What do you normally feed?
Can you please post some photos of the chicks and their poop?
A video of their actions may be helpful - upload video to youtube and provide a link.
You mention head shaking - do you feel it's neurological or could they have lice/mites, ear infection, etc.?
Generally you do not want to give extra vitamins that contain B1 (Thiamine) when treating with Corid (amprolium).
Plumb's Vet Drug Manual has this notation in the contraindications section under Amprolium --- "excessive thiamine in the diet can reduce or reverse the anticoccidial activity of the drug"
I have found nothing defines "excessive" - so for me, I would not give additional vitamin B1 (Thiamine) while using Amprolium.