Post concussion syndrome is separate and distinct from spine injury but both can occur in the same accident. Post concussion syndrome (PCS) is considered a shearing injury of the brain components (nerves and surrounding supporting tissues) that causes brain dysfunction. Normally, the symptoms are as you note and typically resolve after some time. If they do not resolve, a visit with a neuropsychologist or psychiatrist would be in order.
I am not a fan of full time brace wear. This device may stabilize your spine but at the expense of muscle deconditioning. A thorough rehabilitation program would be a better investment.
Your neck pain could be from injury to the spinal structures. You are now two years out from this injury with significant symptoms and I think you need a consultation with a spine surgeon and a neuropsychologist.