Poor you.
Please come over to the TBI/PCS forum and have a chat with all of us MVA veterans. So much of what can happen, isn't apparent for sometime after the actual collision.
My first bit of advice is, trust your body, not the doctors. If you're an American, you might want to consider doing a free consult with a personal injury lawyer. In the interim, you probably don't want to sign anything or even speak a word to the other side's insurance people.